Physiology and Hygiene for Secondary Schools
by Francis M. Walters, A.M.
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Physiology and Hygiene for Secondary Schools

by Francis M. Walters, A.M.

Edition 1, (November 15, 2005)

D.C. Heath and Co. - Publishers

Original copyright 1909

"It is quite possible to give instruction in this subject in such a manner as not only to confer knowledge which is useful in itself, but to serve the purpose of a training in accurate observation, and in the methods of reasoning of physical science."—Huxley.


The aim in the preparation of this treatise on the human body has been, first, to set forth in a teachable manner the actual science of physiology; and second, to present the facts of hygiene largely as applied physiology. The view is held that "right living" consists in the harmonious adjustment of one's habits to the nature and plan of the body, and that the best preparation for such living is a correct understanding of the physical self. It is further held that the emphasizing of physiology augments in no small degree the educative value of the subject, greater opportunity being thus afforded for exercise of the reasoning powers and for drill in the modus operandi of natural forces. In the study of physiology the facts of anatomy have a place, but in an elementary course these should be restricted to such as are necessary for revealing the general structure of the body.

Although no effort has been spared to bring this work within the comprehension of the pupil, its success in the classroom will depend largely upon the method of handling the subject by the teacher. It is recommended, therefore, that the relations which the different organs and processes sustain to each other, and to the body as a whole, be given special prominence. The pupil should be impressed with the essential unity of the body and should see in the diversity of its activities the serving of a common purpose. In creating such an impression the introductory paragraphs at the beginning of many of the chapters and the summaries throughout the book, as well as the general arrangement of the subject-matter, will be found helpful.

Since the custom largely prevails of teaching physiology in advance of the sciences upon which it rests—biology, physics, and chemistry—care should be exercised to develop correct ideas of the principles and processes derived from these sciences. Too much latitude has been taken in the past in the use of comparisons and illustrations drawn from "everyday life." To teach that the body is a "house," "machine," or "city"; that the nerves carry "messages"; that the purpose of oxygen is to "burn up waste"; that breathing is to "purify the blood," etc., may give the pupil phrases which he can readily repeat, but teaching of this kind does not give him correct ideas of his body.

The method of teaching, however, that uses the pupil's experience as a basis upon which to build has a value not to be overlooked. The fact that such expressions as those quoted above are so easily remembered proves the value of connecting new knowledge with the pupil's experience. But the inadequacy of this experience must be recognized and taken into account. The concepts of the average pupil are entirely too indefinite and limited to supply the necessary foundation for a science such as physiology. Herein lies the great value of experiments and observations. They supplement the pupil's experience, and increase both the number and definiteness of his concepts. No degree of success can be attained if this phase of the study is omitted.

The best results in physiology teaching are of course attained where laboratory work is carried on by the pupils, but where this cannot be arranged, class experiments and observations must suffice. The Practical Work described at the close of most of the chapters is mainly for class purposes. While these serve a necessary part in the development of the subject, it is not essential that all of the experiments and observations be made, the intention being to provide for some choice on the part of the teacher. A note-book should be kept by the pupil.

To adapt the book to as wide a range of usefulness as possible, more subject-matter is introduced than is usually included in an elementary course. Such portions, however, as are unessential to a proper understanding of the body by the pupil are set in small type, to be used at the discretion of the teacher.

The use of books of reference is earnestly recommended. For this purpose the usual high school texts may be employed to good advantage. A few more advanced works should, however, be frequently consulted. For this purpose Martin's Human Body (Advanced Course), Rettger's Advanced Lessons in Physiology, Thornton's Human Physiology, Huxley's Lessons in Elementary Physiology, Howell's A Text-book of Physiology, Hough and Sedgwick's Hygiene and Sanitation, and Pyle's Personal Hygiene will be found serviceable.

In the preparation of this work valuable assistance has been rendered by Dr. C.N. McAllister, Department of Psychology, and by Professor B.M. Stigall, Department of Biology, along the lines of their respective specialties, and in a more general way by President W.J. Hawkins and others of the Warrensburg, Missouri, State Normal School. Expert advice from Professor S.D. Magers, Instructor in Physiology and Bacteriology, State Normal School, Ypsilanti, Michigan, has been especially helpful, and many practical suggestions from the high school teachers of physiology of Kansas City, Missouri, Professor C.H. Nowlin, Central High School, Dr. John W. Scott, Westport High School, and Professor A.E. Shirling, Manual Training High School, all of whom read both manuscript and proofs, have been incorporated. Considerable material for the Practical Work, including the respiration experiment (page 101) and the reaction time experiment (page 323), were contributed by Dr. Scott. Professor Nowlin's suggestions on subject-matter and methods of presentation deserve special mention. To these and many others the author makes grateful acknowledgment.








To derive strength equal to the daily task; to experience the advantages of health and avoid the pain, inconvenience, and danger of disease; to live out contentedly and usefully the natural span of life: these are problems that concern all people. They are, however, but different phases of one great problem—the problem of properly managing or caring for the body. To supply knowledge necessary to the solution of this problem is the chief reason why the body is studied in our public schools.

*Divisions of the Subject.*—The body is studied from three standpoints: structure, use of parts, and care or management. This causes the main subject to be considered under three heads, known as anatomy, physiology, and hygiene.

Anatomy treats of the construction of the body—the parts which compose it, what they are like, and where located. Its main divisions are known as gross anatomy and histology. Gross anatomy treats of the larger structures of the body, while histology treats of the minute structures of which these are composed—parts too small to be seen with the naked eye and which have to be studied with the aid of the microscope.

Physiology treats of the function, or use, of the different parts of the body—the work which the parts do and how they do it—and of their relations to one another and to the body as a whole.

Hygiene treats of the proper care or management of the body. In a somewhat narrower sense it treats of the "laws of health." Hygiene is said to be personal, when applied by the individual to his own body; domestic, when applied to a small group of people, as the family; and public, or general, when applied to the community as a whole or to the race.

*The General Aim of Hygiene.*—There are many so-called laws of health, and for these laws it is essential in the management of the body to find a common basis. This basic law, suggested by the nature of the body and conditions that affect its well-being, may be termed the Law of Harmony: The mode of living must harmonize with the plan of the body. To live properly one must supply the conditions which his body, on account of its nature and plan, requires. On the other hand, he must avoid those things and conditions which are injurious, i.e., out of harmony with the body plan. To secure these results, it is necessary to determine what is and what is not in harmony with the plan of the body, and to find the means of applying this knowledge to the everyday problems of living. Such is the general aim of hygiene. Stated in other words: Hygiene has for its general aim the bringing about of an essential harmony between the body and the things and conditions that affect it.(1)

*Relation of Anatomy and Physiology to the Study of Hygiene.*—If the chief object in studying the body is that of learning how to manage or care for it, and hygiene supplies this information, why must we also study anatomy and physiology? The answer to this question has already been in part suggested. In order to determine what things and conditions are in harmony with the plan of the body, we must know what that plan is. This knowledge is obtained through a study of anatomy and physiology. The knowledge gained through these subjects also renders the study of hygiene more interesting and valuable. One is enabled to see why and how obedience to hygienic laws benefits, and disobedience to them injures, the body. This causes the teachings of hygiene to be taken more seriously and renders them more practical. In short, anatomy and physiology supply a necessary basis for the study of hygiene.

*Advantages of Properly Managing the Body.*—One result following the mismanagement of the body is loss of health. But attending the loss of health are other results which are equally serious and far-reaching. Without good health, people fail to accomplish their aims and ambitions in life; they miss the joy of living; they lose their ability to work and become burdens on their friends or society. The proper management of the body means health, and it also means the capacity for work and for enjoyment. Not only should one seek to preserve his health from day to day, but he should so manage his body as to use his powers to the best advantage and prolong as far as possible the period during which he may be a capable and useful citizen.


*External Divisions.*—Examined from the outside, the body presents certain parts, or divisions, familiar to all. The main, or central, portion is known as the trunk, and to this are attached the head, the upper extremities, and the lower extremities. These in turn present smaller divisions which are also familiar. The upper part of the trunk is known as the thorax, or chest, and the lower part as the abdomen. The portions of the trunk to which the arms are attached are the shoulders, and those to which the legs are joined are the hips, while the central rear portion between the neck and the hips is the back. The fingers, the hand, the wrist, the forearm, the elbow, and the upper arm are the main divisions of each of the upper extremities. The toes, the foot, the ankle, the lower leg, the knee, and the thigh are the chief divisions of each of the lower extremities. The head, which is joined to the trunk by the neck, has such interesting parts as the eyes, the ears, the nose, the jaws, the cheeks, and the mouth. The entire body is inclosed in a double covering, called the skin, which protects it in various ways.

*The Tissues.*—After examining the external features of the body, we naturally inquire about its internal structures. These are not so easily investigated, and much which is of interest to advanced students must be omitted from an elementary course. We may, however, as a first step in this study, determine what kinds of materials enter into the construction of the body. For this purpose the body of some small animal should be dissected and studied. (See observation at close of chapter.) The different materials found by such a dissection correspond closely to the substances, called tissues, which make up the human body. The main tissues of the body, as ordinarily named, are the muscular tissue, the osseous tissue, the connective tissue, the nervous tissue, the adipose tissue, the cartilaginous tissue, and the epithelial and glandular tissue. Most of these present different varieties, making all together some fifteen different kinds of tissues that enter into the construction of the body.(2)

*General Purposes of the Tissues.*—The tissues, first of all, form the body. As a house is constructed of wood, stone, plaster, iron, and other building materials, so is the body made up of its various tissues. For this reason the tissues have been called the building materials of the body.

In addition to forming the body, the tissues supply the means through which its work is carried on. They are thus the working materials of the body. In serving this purpose the tissues play an active role. All of them must perform the activities of growth and repair, and certain ones (the so-called active tissues) must do work which benefits the body as a whole.

*Purposes of the Different Tissues.*—In the construction of the body and also in the work which it carries on, the different tissues are made to serve different purposes. The osseous tissue is the chief substance in the bony framework, or skeleton, while the muscular tissue produces the different movements of the body. The connective tissue, which is everywhere abundant, serves the general purpose of connecting the different parts together. Cartilaginous tissue forms smooth coverings over the ends of the bones and, in addition to this, supplies the necessary stiffness in organs like the larynx and the ear. The nervous tissue controls the body and brings it into proper relations with its surroundings, while the epithelial tissue (found upon the body surfaces and in the glands) supplies it with protective coverings and secretes liquids. The adipose tissue (fat) prevents the too rapid escape of heat from the body, supplies it with nourishment in time of need, and forms soft pads for delicate organs like the eyeball.

*Properties of the Tissues.*—If we inquire how the tissues are able to serve such widely different purposes, we find this answer. The tissues differ from one another both in composition and in structure and, on this account, differ in their properties.(3) Their different properties enable them to serve different purposes in the body. Somewhat as glass is adapted by its transparency, hardness, and toughness to the use made of it in windows, the special properties of the tissues adapt them to the kinds of service which they perform. Properties that adapt tissues to their work in the body are called essential properties. The most important of these essential properties are as follows:

1. Of osseous tissue, hardness, stiffness, and toughness. 2. Of muscular tissue, contractility and irritability. 3. Of nervous tissue, irritability and conductivity. 4. Of cartilaginous tissue, stiffness and elasticity. 5. Of connective tissue, toughness and pliability. 6. Of epithelial tissue, ability to resist the action of external forces and power to secrete.

[Fig. 1]

Fig. 1—Hand and forearm, showing the grouping of muscular and connective tissues in the organ for grasping.

*Tissue Groups.*—In the construction of the body the tissues are grouped together to form its various divisions or parts. A group of tissues which serves some special purpose is known as an organ. The hand, for example, is an organ for grasping (Fig. 1). While the different organs of the body do not always contain the same tissues, and never contain them in the same proportions, they do contain such tissues as their work requires and these have a special arrangement—one adapted to the work which the organs perform.

In addition to forming the organs, the tissues are also grouped in such a manner as to provide supports for organs and to form cavities in which organs are placed. The various cavities of the body are of particular interest and importance. The three largest ones are the cranial cavity, containing the brain; the thoracic cavity, containing the heart and the lungs; and the abdominal cavity, containing the stomach, the liver, the intestines, and other important organs (Fig. 2). Smaller cavities serving different purposes are also found.

[Fig. 2]

Fig. 2—Diagram of a lengthwise section of the body to show its large cavities and the organs which they contain.

*Organs and Systems.*—The work of the body is carried on by its various organs. Many, in fact the majority, of these organs serve more than one purpose. The tongue is used in talking, in masticating the food, and in swallowing. The nose serves at least three distinct purposes. The mouth, the arms, the hands, the feet, the legs, the liver, the lungs, and the stomach are also organs that serve more than one purpose. This introduces the principle of economy into the construction of the body and diminishes the number of organs that would otherwise be required.

The various organs also combine with one another in carrying on the work of the body. An illustration of this is seen in the digestion of the food—a process which requires the combined action of the mouth, stomach, liver, intestines, and other organs. A number of organs working together for the same purpose form a system. The chief systems of the body are the digestive system, the circulatory system, the respiratory system, the muscular system, and the nervous system.

*The Organ and its Work.*—A most interesting question relating to the work of the organ is this: Does the organ work for its own benefit or for the benefit of the body as a whole? Does the hand, for example, grasp for itself or in order that the entire body may come into possession? Only slight study is sufficient to reveal the fact that each organ performs a work which benefits the body as a whole. In other words, just as the organ itself is a part of the body, the work which it does is a part of the necessary work which the body has to do.

But in working for the general good, or for the body as a whole, each organ becomes a sharer in the benefits of the work done by every other organ. While the hand receives only a little of the nourishment contained in the food which it places in the mouth or of the heat from, fuel which it places on the fire, it is aided and supported by the work of all the other organs of the body—eyes, feet, brain, heart, etc. The hand does not and cannot work independently of the other organs. It is one of the partners in a very close combination where, by doing a particular work, it, shares in the profits of all. What is true of the hand is true of every other organ of the body.

*An Organization.*—The relations which the different organs sustain to each other and to the body as a whole suggest the possibility of classifying the body as an organization. This term is broadly applied to a variety of combinations. An organization is properly defined as any group of individuals which, in working together for a common purpose, practices the division of labor. This definition will be better understood by considering a few familiar examples.

A baseball team is an organization. The team is made up of individual players. These work together for the common purpose of winning games. They practice the division of labor in that the different players do different things—one catching, another pitching, and so on. A manufacturing establishment which employs several workmen may also be an organization. The article manufactured provides the common purpose toward which all strive; and, in the assignment of different kinds of work to the individual workmen, the principle of division of labor is carried out. For the same reason a school, a railway system, an army, and a political party are organizations.

An organization of a lower order of individuals than these human organizations is to be found in a hive of bees. This is made up of the individual bees, and these, in carrying on the general work of the hive, are known to practice the division of labor.

*Is the Body an Organization*?—If the body is an organization, it must fulfill the conditions of the definition. It must be made up of separate or individual parts. These must work together for the same general purpose, and, in the accomplishment of this purpose, must practice the division of labor. That the body practices the division of labor is seen in the related work of the different organs. That it is made up of minute, but individual, parts will be shown in the chapter following. That it carries on a general work which is accomplished through the combined action of its individual parts is revealed through an extended study of its various activities. The body is an organization. Moreover, it is one of the most complex and, at the same time, most perfect of the organizations of which we have knowledge.

*Summary.*—Viewed from the outside, the body is seen to be made up of divisions which are more or less familiar. Viewed internally, it is found to consist of different kinds of materials, called tissues. The tissues are adapted, by their properties, to different purposes both in the construction of the body and in carrying on its work. The working parts of the body are called organs and these in their work combine to form systems. The entire body, on account of the method of its construction and the character of its work, may be classed as an organization.

*Exercises.*—1. Name and locate the chief external divisions of the body.

2. What tissues may be found by dissecting the leg of a chicken?

3. Name the most important properties and the most important uses of muscular tissue, osseous tissue, and connective tissue.

4. Define an organ. Define a system. Name examples of each.

5. Name the chief cavities of the body and the organs which they contain.

6. What tissues are present in the hand? How does each of these aid in the work of the hand?

7. Define an organization. Show that a railway system, an army, and a school are organizations.

8. What is meant by the phrase "division of labor"? In what manner is the division of labor practiced in a shoe or watch factory? What are the advantages?

9. What are the proofs that the body is an organization?


*Observation on the Tissues.*—Examine with care the structures in the entire leg of a chicken, squirrel, rabbit, or other small animal used for food. Observe, first of all, the external covering, consisting of cuticle and hair, claws, scales, or feathers, according to the specimen. These are similar in structure, and they form the epidermis, which is one kind of epithelial tissue. With a sharp knife lay open the skin and observe that it is attached to the parts underneath by thin, but tough, threads and sheaths. These represent a variety of connective tissue. The reddish material which forms the greater portion of the specimen is a variety of muscular tissue, and its divisions are called muscles. With a blunt instrument, separate the muscles, by tearing apart the connective tissue binding them together, and find the glistening white strips of connective tissue (tendons) which attach them to the bones. Find near the central part of the leg a soft, white cord (a nerve) which represents one variety of nervous tissue. The bones, which may now be examined, form the osseous tissue. At the ends of the bones will be found a layer of smooth, white material which represents one kind of cartilaginous tissue. The adipose, or fatty, tissue, which is found under the skin and between the other tissues, is easily recognized.

*Relation of the Tissues to the Organs.*—Observe in the specimen just studied the relation of the different tissues to the organ as a whole (regarding the leg as an organ), i.e., show how each of the tissues aids in the work which the organ accomplishes. Show in particular how the muscles supply the foot with motion, by tracing out the tendons that connect them with the toes. Pull on the different tendons, noting the effect upon the different parts of the foot.


What is the nature of the body organization? What are the individual parts, or units, that make it up? What general work do these carry on and upon what basis do they practice the division of labor? The answers to these questions will suggest the main problems in the study of the body.

[Fig. 3]

Fig. 3—Diagram showing the relation of the cells and the intercellular material. C. Cells. I. Intercellular material.

*Complex Nature of the Tissues.*—To the unaided eye the tissues have the appearance of simple structures. The microscope, however, shows just the reverse to be true. When any one of the tissues is suitably prepared and carefully examined with this instrument, at least two classes of materials can be made out. One of these consists of minute particles, called cells; the other is a substance lying between the cells, known as the intercellular material (Fig. 3). The cells and the intercellular material, though varying in their relative proportions, are present in all the tissues.

*The Body a Cell Group.*—The biologist has found that the bodies of all living things, plants as well as animals, consist either of single cells or of groups of cells. The single cells live independently of one another, but the cells that form groups are attached to, and are more or less dependent upon, one another. In the first condition are found the very lowest forms of life. In the second, life reaches its greatest development. The body of man, which represents the highest type of life, is recognized as a group of cells. In this group each cell is usually separate and distinct from the others, but is attached to them, and is held in place by the intercellular material.

*Protoplasm, the Cell Substance.*—The cell is properly regarded as an organized bit of a peculiar material, called protoplasm. This is a semi-liquid and somewhat granular substance which resembles in appearance the white of a raw egg. Its true nature and composition are unknown, because any attempt to analyze it kills it, and dead protoplasm is essentially different from living protoplasm. It is known, however, to be a highly complex substance and to undergo chemical change readily. It appears to be the only kind of matter with which life is ever associated, and for this reason protoplasm is called the physical basis of life. Its organization into separate bits, or cells, is necessary to the life activities that take place within it.

*Structure of the Cell.*—Though all portions of the cell are formed from the protoplasm, this essential substance differs both in structure and in function at different places in the cell. For this reason the cell is looked upon as a complex body having several distinct parts. At or near the center is a clear, rounded body, called the nucleus. This plays some part in the nourishment of the cell and also in the formation of new cells. If it be absent, as is sometimes the case, the cell is short-lived and unable to reproduce itself. The variety of protoplasm contained in the nucleus is called the nucleoplasm.

[Fig. 4]

Fig. 4—Diagram of a typical cell (after Wilson). 1. Main body. 2. Nucleus. 3. Attraction sphere. 4. Food particles and waste. 5. Cell-wall. 6. Masses of active material found in certain cells, called plastids.

Surrounding the nucleus is the main body of the cell, sometimes referred to as the "protoplasm." Since the protoplasm forms all parts of the cell, this substance is more properly called the cytoplasm, or cell plasm. Surrounding and inclosing the cytoplasm, in many cells, is a thin outer layer, or membrane, which affords more or less protection to the contents of the cell. This is usually referred to as the cell-wall. A fourth part of the cell is also described, being called the attraction sphere. This is a small body lying near the nucleus and cooeperating with that body in the formation of new cells. Food particles, wastes, and other substances may also be present in the cytoplasm. The parts of a typical cell are shown in Fig. 4.

*Importance of the Cells.*—The cells must be regarded as the living, working parts of the body. They are the active agents in all of the tissues, enabling them to serve their various purposes. Working through the tissues, they build up the body and carry on its different activities. They are recognized on this account as the units of structure and of function, and are the "individuals" in the body organization. Among the most important and interesting of the activities of the cells are those by which they build up the body, or cause it to grow.

*How the Cells enable the Body to Grow.*—Every cell is able to take new material into itself and to add this to the protoplasm. This tends to increase the amount of the protoplasm, thereby causing the cells to increase in size. A general increase in the size of the cells has the effect of increasing the size of the entire body, and this is one way by which they cause it to grow. There is, however, a fixed limit, varying with different cells, to the size which they attain, and this is quite low. (The largest cells are scarcely visible to the naked eye.) Any marked increase in the size of the body must, therefore, be brought about by other means. Such a means is found in the formation of new cells, or cell reproduction. The new cells are always formed by and from the old cells, the essential process being known as cell-division.

[Fig. 5]

Fig. 5—Steps in cell-division (after Wilson). Note that the process begins with the division of the attraction sphere, then involves the nucleus, and finally separates the main body.

*Cell-Division.*—By dividing, a single cell will, on attaining its growth, separate into two or more new cells. The process is quite complex and is imperfectly understood. It is known, however, that the act of separation is preceded by a series of changes in which the attraction sphere and the nucleus actively participate, and that, as a result of these changes, the contents of the old cell are rearranged to form the new cells. Some of the different stages in the process, as they have been studied under the microscope, are indicated in Fig. 5.

Gradually, through the formation of new cells and by the growth of these cells after they have been formed, the body attains its full size. When growth is complete, cell reproduction is supposed to cease except where the tissues are injured, as in the breaking of a bone, or where cells, like those at the surface of the skin, are subject to wear. Then new material continues to be added to the protoplasm throughout life, but in amount only sufficient to replace that lost from the protoplasm as waste.

[Fig. 6]

Fig. 6—A tumbler partly filled with marbles covered with water, suggesting the relations of the cells to the lymph.

*Cell Surroundings.*—All cells are said to be aquatic. This means simply that they require water for carrying on their various activities. The cells, in order to live, must take in and give out materials, and water is necessary to both processes. It is also an essential part of the protoplasm. Deprived of water, cells become inactive and usually die. Aquatic surroundings are provided for the cells of the body through a liquid known as the lymph, which is distributed throughout the intercellular material (Fig. 6). This consists of water containing oxygen and food substances in solution. Besides supplying these to the cells, the lymph also receives their wastes. Through the lymph the necessary conditions for cell life are provided in the body.

*The General Work of Cells.*—In handling the materials derived from the lymph, the cells carry on three well-defined processes, known as absorption, assimilation, and excretion.

Absorption is the process of taking water, food, and oxygen into the cells.

Assimilation is a complex process which results in the addition of the absorbed materials to the protoplasm. Through assimilation the protoplasm is built up or renewed.

Excretion is the throwing off of such waste materials as have been formed in the cells. These are passed into the lymph and thence to the surface of the body.

Absorption, assimilation, excretion, and also reproduction are performed by all classes of cells. They are, on this account, referred to as the general work of cells.

*The Special Work of Cells.*—In addition to the general work which all cells do in common, each class of cells in the body is able to do some particular kind of work—a work which the others cannot do or which they can do only to a limited extent. This is spoken of as the special work of cells. Examples of the special work of cells are found in the production of motion by muscle cells and in the secretion of liquids by gland cells. It may be noted that while the general work of cells benefits them individually, their special work benefits the body as a whole. Another example of the special work of cells is found in the

[Fig. 7]

Fig. 7—Cartilage cells, surrounded by the intercellular material which they have deposited.

*Production of the Intercellular Material.*—Though most of the cells of the body deposit to a slight extent this material, the greater part of it is produced by a single class of cells found in bone, cartilage, and connective tissue. Cartilage, bone, and connective tissue differ greatly from the other tissues in the amount of intercellular material which they contain, the difference being due to these cells. In the connective tissue they deposit the fibrous material so important in holding the different parts of the body together. In the cartilage they produce the gristly substance which forms by far its larger portion (Fig. 7). In the bones they deposit a material similar to that in the cartilage, except that with it is mixed a mineral substance which gives the bones their hardness and stiffness.(4) The intercellular material, in addition to connecting the cells, supplies to certain tissues important properties, such as the elasticity of cartilage and the stiffness of the bones.

*Nature of the Body Organization.*—The division of labor carried on by the different organs, as shown in the preceding chapter, is in reality carried on by the cells that form the organs. To see that this is true we have only to observe the relation of cells to tissues and of tissues to organs. The cells form the tissues and the tissues form the organs. This arrangement enables the special work of different kinds of cells to be combined in the work of the organ as a whole. This is seen in the hand which, in grasping, uses motion supplied by the muscle cells, a controlling influence supplied by the nerve cells, a framework supplied by the bone cells, and so on. The cells supply the basis for the body organization and, properly speaking, the body is an organization of cells(5) (Recall the definition of an organization, page 10.) In this organization there are to be observed:

1. A definite arrangement of the cells to form the tissues. A tissue is a group of like cells.

2. A definite arrangement of the tissues in the organ. Each organ contains the tissues needed for its work.

3. In several instances there is a definite arrangement of organs to form systems.

4. The body as a whole is made up of organs and systems, together with the structures necessary for their support and protection.

There now remains a further question for consideration. What is the one supreme end, or purpose, toward which all the activities of the body organization are directed? This purpose will naturally have some relation to the maintenance, or preservation, of the cell group which we call the body.

*The Maintenance of Life.*—The preservation of any cell group in its natural condition, whether it be plant or animal, is accomplished through keeping it alive. If life ceases, the group quickly disintegrates and its elements become scattered, a fact which is verified through everyday observation. Though the nature of life is unknown, it may be looked upon as the organizer and preserver of the protoplasm. But in preserving the protoplasm it also preserves the entire cell group, or body. Life is thus the most essential condition of the body. With life all portions of the body are concerned, and toward its maintenance all the activities of the body organization are directed.

*The Nutrient Fluid in its Relations to the Cells.*—The maintenance of life within the cells requires, as we have seen, that they be supplied with water, food, and oxygen, and that they be relieved of such wastes as they form. This double purpose is accomplished through the agency of an internal nutrient fluid, a portion of which has already been referred to as the lymph. Not only does this fluid supply the means for keeping the cells alive, but, through the cells, it is also the means of preserving the life of the body as a whole.

The cells, however, rapidly exhaust the nutrient fluid. They take from it food and oxygen and they put into it their wastes. To prevent its becoming unfit for supplying their needs, food and oxygen must be continually added to this fluid, and waste materials must be continually removed. This is not an easy task. As a matter of fact, the preparation, distribution, and purification of the nutrient fluid requires the direct or indirect aid of practically all parts of the body. It supplies for this reason a broad basis for the division of labor on the part of the cells.

*Relation of the Body to its Environment.*—While life is directly dependent upon the internal nutrient fluid, it is indirectly dependent upon the physical surroundings of the body. Herein lies the need of the external organs—the feet and legs for moving about, the hands for handling things, the eyes for directing movements, etc. That the great needs of the body are supplied from its surroundings are facts of common experience. Food, shelter, air, clothing, water, and the means of protection are external to the body and form a part of its environment. In making the things about him contribute to his needs, man encounters a problem which taxes all his powers. Only by toil and hardship, "by the sweat of his brow," has he been able to wrest from his surroundings the means of his sustenance.

*The Main Physiological Problems.*—The study of the body is thus seen to resolve itself naturally into the consideration of two main problems:

1. That of maintaining in the body a nutrient fluid for the cells.

2. That of bringing the body into such relations with its surroundings as will enable it to secure materials for the nutrient fluid and satisfy its other needs.

The first problem is internal and includes the so-called vital processes, known as digestion, circulation, respiration, and excretion. The second problem is external, as it were, and includes the work of the external organs—the organs of motion and of locomotion and the organs of special sense. These problems are closely related, since they are the two divisions of the one problem of maintaining life. Neither can be considered independently of the other. In the chapter following is taken up the first of these problems.

*Summary.*—The individual parts, or units, that form the body organization are known as cells. These consist of minute but definitely arranged portions of protoplasm and are held together by the intercellular material. They build up the body and carry on its different activities. The tissues are groups of like cells. By certain general activities the cells maintain their existence in the tissues and by the exercise of certain special activities they adapt the tissues to their purposes in the body. The body, as a cell organization, has its activities directed under normal conditions toward a single purpose—that of maintaining life. In the accomplishment of this purpose a nutrient fluid is provided for the cells and proper relations between the body and its surroundings are established.

*Exercises.*—1. If a tissue be compared to a brick wall, to what do the separate bricks correspond? To what the mortar between the bricks?

2. Draw an outline of a typical cell, locating and naming the main divisions.

3. How do the cells enable the body to grow? Describe the process of cell-division.

4. How does the general work of cells differ from their special work? Define absorption, excretion, and assimilation as applied to the cells.

5. Compare the conditions surrounding a one-celled animal, living in water, to the conditions surrounding the cells in the body.

6. What is meant by the term "environment"? How does man's environment differ from that of a fish?

7. What is the necessity for a nutrient fluid in the body?

8. Why is the maintenance of life necessarily the chief aim of all the activities of the body?

9. State the two main problems in the study of the body.


*Observations.*—1. Make some scrapings from the inside of the cheek with a dull knife and mix these with a little water on a glass slide. Place a cover-glass on the same and examine with a compound microscope. The large pale cells that can be seen in this way are a variety of epithelial cells.

2. Mount in water on a glass slide some thin slices of cartilage and examine first with a low and then with a high power of microscope. (Suitable slices may be cut, with a sharp razor, from the cartilage found at the end of the rib of a young animal.) Note the small groups of cells surrounded by, and imbedded in, the intercellular material.

3. Mount and examine with the microscope thin slices of elder pith, potato, and the stems of growing plants. Make drawings of the cells thus observed.

4. Examine with the microscope a small piece of the freshly sloughed off epidermis of a frog's skin. Examine it first in its natural condition, and then after soaking for an hour or two in a solution of carmine. Make drawings.

5. Mount on a glass slide some of the scum found on stagnant water and examine it with a compound microscope. Note the variety and relative size of the different things moving about. The forms most frequently seen by such an examination are one-celled plants. Many of these have the power of motion.

6. Examine tissues of the body, such as nervous, muscular, and glandular tissues, which have been suitably prepared and mounted for microscopic study, using low and high powers of the microscope. Make drawings of the cells in the different tissues thus observed.


Two liquids of similar nature are found in the body, known as the blood and the lymph. These are closely related in function and together they form the nutrient fluid referred to in the preceding chapter. The blood is the more familiar of the two liquids, and the one which can best be considered at this time.

*The Blood: where Found.*—The blood occupies and moves through a system of closed tubes, known as the blood vessels. By means of these vessels the blood is made to circulate through all parts of the body, but from them it does not escape under normal conditions. Though provisions exist whereby liquid materials may both enter and leave the blood stream, it is only when the blood vessels are cut or broken that the blood, as blood, is able to escape from its inclosures.

*Physical Properties of the Blood.*—Experiments such as those described at the close of this chapter reveal the more important physical properties of the blood. It may be shown to be heavier and denser than water; to have a faint odor and a slightly salty taste; to have a bright red color when it contains oxygen and a dark red color when oxygen is absent; and to undergo, when exposed to certain conditions, a change called coagulation. These properties are all accounted for through the different materials that enter into the formation of the blood.

[Fig. 8]

Fig. 8—Blood corpuscles, highly magnified. A. Red corpuscles as they appear in diluted blood. B. Arrangement of red corpuscles in rows between which are white corpuscles, as may be seen in undiluted blood. C. Red corpuscles much enlarged to show the form.

*Composition of the Blood.*—To the naked eye the blood appears as a thick but simple liquid; but when examined with a compound microscope, it is seen to be complex in nature, consisting of at least two distinct portions. One of these is a clear, transparent liquid; while the other is made up of many small, round bodies that float in the liquid. The liquid portion of the blood is called the plasma; the small bodies are known as corpuscles. Two varieties of corpuscles are described—the red corpuscles and the white corpuscles (Fig. 8). Other round particles, smaller than the corpuscles, may also be seen under favorable conditions. These latter are known as blood platelets.

*Red Corpuscles.*—The red corpuscles are classed as cells, although, as found in the blood of man and the other mammals (Fig. 9), they have no nuclei.(6) Each one consists of a little mass of protoplasm, called the stroma, which contains a substance having a red color, known as hemoglobin. The shape of the red corpuscle is that of a circular disk with concave sides. It has a width of about 1/3200 of an inch (7.9 microns(7)) and a thickness of about 1/13000 of an inch (1.9 microns). The red corpuscles are exceedingly numerous, there being as many as five millions in a small drop (one cubic millimeter) of healthy blood. But the number varies somewhat and is greatly diminished during certain forms of disease.

[Fig. 9]

Fig. 9—Red corpuscles from various animals. Those from mammals are without nuclei, while those from birds and cold-blooded animals have nuclei.

It is the function of the red corpuscles to serve as oxygen carriers for the cells. They take up oxygen at the lungs and release it at the cells in the different tissues.(8) The performance of this function depends upon the hemoglobin.

*Hemoglobin.*—This substance has the remarkable property of forming, under certain conditions, a weak chemical union with oxygen and, when the conditions are reversed, of separating from it. It forms about nine tenths of the solid matter of the red corpuscles and to it is due the colors of the blood. When united with the oxygen it forms a compound, called oxyhemoglobin, which has a bright red color; the hemoglobin alone has a dark red color. These colors are the same as those of the blood as it takes on and gives off oxygen. The stroma, which forms only about one tenth of the solid matter of the corpuscles, serves as a contrivance for holding the hemoglobin. The conditions which cause the hemoglobin to unite with oxygen in the lungs and to separate from it in the tissues, will be considered later (Chapter VIII).

*Disappearance and Origin of Red Corpuscles.*—The red corpuscles, being cells without nuclei, are necessarily short-lived. It has been estimated that during a period of one to two months, all the red corpuscles in the body at a given time will have disappeared and their places taken by new ones. The origin of new corpuscles, however, and the manner of ridding the blood of old ones are problems that are not as yet fully solved. The removal of the products of broken down corpuscles is supposed to take place both in the liver and in the spleen.(9)

Regarding the origin of the red corpuscles, the evidence now seems conclusive that large numbers of them are formed in the red marrow of the bones. The red marrow is located in what is known as the spongy substance of the bones (Chapter XIV) and consists, to a large extent, of cells somewhat like the red corpuscles, but differing from them in having nuclei. These appear to be constantly in a state of reproduction. The blood, flowing through the minute cavities containing these cells, carries those that have been loosened out into the blood stream. Nuclei appear in the red corpuscles at the time of their formation, but these quickly separate and, according to some authorities, form the blood platelets.

*White Corpuscles.*—The white corpuscles, or leucocytes, are cells of a general spherical shape, each containing one, two, or more nuclei. They are much less numerous than the red, there being on the average only one white corpuscle to about every five hundred of the red ones. On the other hand, the white corpuscles are larger than the red, one of the former being equal in volume to about three of the latter.

[Fig. 10]

Fig. 10—*Escape of white corpuscles from a small blood vessel* (Hall). At A the conditions are normal, but at B some excitation in the surrounding tissue leads to a migration of corpuscles. 1, 2, and 3 show different stages of the passage.

The white corpuscles are found, when studied under favorable conditions, to possess the power of changing their shape and, by this means, of moving from place to place. This property enables them to penetrate the walls of capillaries and to pass with the lymph in between the cells of the tissues. The white corpuscles are, therefore, not confined to the blood vessels, as are the red corpuscles, but migrate through the intercellular spaces (Fig. 10). If any part of the body becomes inflamed, the white corpuscles collect there in large numbers; and, on breaking down, they form most of the white portion of the sore, called the pus.

New white corpuscles are formed from old ones, by cell-division. Their production may occur in almost any part of the body, but usually takes place in the lymphatic glands (Chapter VI) and in the spleen, where conditions for their development are especially favorable. In these places they are found in great abundance and in various stages of development.

*Functions of White Corpuscles.*—The main use of the white corpuscles appears to be that of a destroyer of disease germs. These consist of minute organisms that find their way into the body and, by living upon the tissues and fluids and by depositing toxins (poisons) in them, cause different forms of disease. Besides destroying germs that may be present in the blood, the white corpuscles also leave the blood and attack germs that have invaded the cells. By forming a kind of wall around any foreign substance, such as a splinter, that has penetrated the skin, they are able to prevent the spread of germs through the body. In a similar manner they also prevent the germs from boils, abscesses, and sore places in general from getting to and infecting other parts of the body.(10) Another function ascribed to the white corpuscles is that of aiding in the coagulation of the blood (page 31); and still another, of aiding in the healing of wounds.

*Plasma.*—The plasma is a complex liquid, being made up of water and of substances dissolved in the water. The dissolved substances consist mainly of foods for the cells and wastes from the cells.

1. The foods represent the same classes of materials as are taken in the daily fare, i.e., proteids, carbohydrates, fats, and salts (Chapter IX). Three kinds of proteids are found in the plasma, called serum albumin, serum globulin, and fibrinogen. These resemble, in a general way, the white of raw egg, but differ from each other in the readiness with which they coagulate. Fibrinogen coagulates more readily than the others and is the only one that changes in the ordinary coagulation of the blood. The others remain dissolved during this process, but are coagulated by chemical agents and by heat. While all of the proteids probably serve as food for the cells, the fibrinogen, in addition, is a necessary factor in the coagulation of the blood (page 31).

The only representative of the carbohydrates in the plasma is dextrose. This is a variety of sugar, being derived from starch and the different sugars that are eaten. The fat in the plasma is in minute quantities and appears as fine droplets—the form in which it is found in milk. While several mineral salts are present in small quantities in the plasma, sodium chloride, or common salt, is the only one found in any considerable amount. The mineral salts serve various purposes, one of which is to cause the proteids to dissolve in the plasma.

2. The wastes are formed at the cells, whence they are passed by the lymph into the blood plasma. They are carried by the blood until removed by the organs of excretion. The two waste products found in greatest abundance in the plasma are carbon dioxide and urea.

The substances dissolved in the plasma form about 10 per cent of the whole amount. The remaining 90 per cent is water. Practically all the constituents of the plasma, except the wastes, enter the blood from the digestive organs.

*Purposes of Water in the Blood.*—Not only is water the most abundant constituent of the blood; it is, in some respects, the most important. It is the liquefying portion of the blood, holding in solution the constituents of the plasma and floating the corpuscles. Deprived of its water, the blood becomes a solid substance. Through the movements of the blood the water also serves the purpose of a transporting agent in the body. The cells in all parts of the body require water and this is supplied to them from the blood. Water is present in the corpuscles as well as in the plasma and forms about 80 per cent of the entire volume of the blood.

*Coagulation of the Blood.*—If the blood is exposed to some unnatural condition, such as occurs when it escapes from the blood vessels, it undergoes a peculiar change known as coagulation.(11) In this change the corpuscles are collected into a solid mass, known as the clot, thereby separating from a liquid called the serum. The serum, which is similar in appearance to the blood plasma, differs from that liquid in one important respect as explained below.

*Causes of Coagulation.*—Although coagulation affects all parts of the blood, only one of its constituents is found in reality to coagulate. This is the fibrinogen. The formation of the clot and the separation of the serum is due almost entirely to the action of this substance. Fibrinogen is for this reason called the coagulable constituent of the blood. In the plasma the fibrinogen is in a liquid form; but during coagulation it changes into a white, stringy solid, called fibrin. This appears in the clot and is the cause of its formation. Forming as a network of exceedingly fine and very delicate threads (Fig. 11) throughout the mass of blood that is coagulating, the fibrin first entangles the corpuscles and then, by contracting, draws them into the solid mass or clot.(12) The contracting of the fibrin also squeezes out the serum. This liquid contains all the constituents of the plasma except the fibrinogen.

[Fig. 11]

Fig. 11—*Fibrin threads* (after Ranvier). These by contracting draw the corpuscles together and form the clot.

*Fibrin Ferment and Calcium.*—Most difficult of all to answer have been the questions: What causes the blood to coagulate outside of the blood vessels and what prevents its coagulation inside of these vessels? The best explanation offered as yet upon this point is as follows: Fibrinogen does not of itself change into fibrin, but is made to undergo this change by the presence of another substance, called fibrin ferment. This substance is not a regular constituent of the blood, but is formed as occasion requires. It is supposed to result from the breaking down of the white corpuscles, and perhaps also from the blood platelets, when the blood is exposed to unnatural conditions. The formation of the ferment leads in turn to the changing of the fibrinogen into fibrin.

Another substance which is necessary to the process of coagulation is the element calcium. If compounds of calcium are absent from the blood, coagulation does not take place. These are, however, regular constituents of healthy blood. Whether the presence of the calcium is necessary to the formation of the ferment or to the action of the ferment upon the fibrinogen is unknown.

*Purpose of Coagulation.*—The purpose of coagulation is to check the flow of blood from wounds. The fact that the blood is contained in and kept flowing continuously through a system of connected vessels causes it to escape rapidly from the body whenever openings in these vessels are made. Clots form at such openings and close them up, stopping in this way the flow that would otherwise go on indefinitely. Coagulation, however, does not stop the flow of blood from the large vessels. From these the blood runs with too great force for the clot to form within the wound.

*Time Required for Coagulation.*—The rate at which coagulation takes place varies greatly under different conditions. It is influenced strongly by temperature; heat hastens and cold retards the process. It may be prevented entirely by lowering the temperature of the blood to near the freezing point. The presence of a foreign substance increases the rapidity of coagulation, and it has been observed that bleeding from small wounds is more quickly checked by covering them with linen or cotton fibers. The fibers in this case hasten the process of coagulation.

*Quantity of Blood.*—The quantity of blood is estimated to be about one thirteenth of the entire weight of the body. This for the average individual is an amount weighing nearly twelve pounds and having a volume of nearly one and one half gallons. About 46 per cent by volume of this amount is made up of corpuscles and 54 per cent of plasma. Of the plasma about 10 per cent consists of solids and 90 per cent of water, as already stated.

*Functions of the Blood.*—The blood is the great carrying, or distributing, agent in the body. Through its movements (considered in the next chapter) it carries food and oxygen to the cells and waste materials from the cells. Much of the blood may, therefore, be regarded as freight in the process of transportation. The blood also carries, or distributes, heat. Taking up heat in the warm parts of the body, it gives it off at places having a lower temperature. This enables all parts of the body to keep at about the same temperature.

In addition to serving as a carrier, the blood has antiseptic properties, i.e., it destroys disease germs. While this function is mainly due to the white corpuscles, it is due in part to the plasma.(13) Through its coagulation, the blood also closes leaks in the small blood vessels. The blood is thus seen to be a liquid of several functions.

[Fig. 12]

Fig. 12—*A balanced change* in water. The level remains constant although the water is continually changing; suggestive of the changes in the blood.

*Changes in the Blood.*—In performing its functions in the body the blood must of necessity undergo rapid and continuous change. The red corpuscles, whose changes have already been noted, appear to be the most enduring constituents of the blood. The plasma is the portion that changes most rapidly. Yet in spite of these changes the quantity and character of the blood remain practically constant.(14) This is because there is a balancing of the forces that bring about the changes. The addition of various materials to the blood just equals the withdrawal of the same materials from the blood. Somewhat as a vessel of water (Fig. 12) having an inflow and an outflow which are equal in amount may keep always at the same level, the balancing of the intake and outgo of the blood keeps its composition about the same from time to time.

*Hygiene of the Blood.*—The blood, being a changeable liquid, is easily affected through our habits of living. Since it may be affected for ill as well as for good, one should cultivate those habits that are beneficial and avoid those that are harmful in their effects. Most of the hygiene of the blood, however, is properly included in the hygiene of the organs that act upon the blood—a fact which makes it unnecessary to treat this subject fully at this time.

From a health standpoint, the most important constituents of the blood are, perhaps, the corpuscles. These are usually sufficient in number and vigor in the blood of those who take plenty of physical exercise, accustom themselves to outdoor air and sunlight, sleep sufficiently, and avoid the use of injurious drugs. On the other hand, they are deficient in quantity and inferior in quality in the bodies of those who pursue an opposite course. Impurities not infrequently find their way into the blood through the digestive organs. One should eat wholesome, well-cooked food, drink freely of pure water, and limit the quantity of food to what can be properly digested. The natural purifiers of the blood are the organs of excretion. The skin is one of these and its power to throw off impurities depends upon its being clean and active.

*Effect of Drugs.*—Certain drugs and medicines, including alcohol and quinine,(15) have recently been shown to destroy the white corpuscles. The effect of such substances, if introduced in considerable amount in the body, is to render one less able to withstand attacks of disease. Many patent medicines are widely advertised for purifying the blood. While these may possibly do good in particular cases, the habit of doctoring one's self with them is open to serious objection. Instead of taking drugs and patent medicines for purifying the blood, one should study to live more hygienically. We may safely rely upon wholesome food, pure water, outdoor exercise and sunlight, plenty of sleep, and a clean skin for keeping the blood in good condition. If these natural remedies fail, a physician should be consulted.

*Summary.*—The blood is the carrying or transporting agent of the body. It consists in part of constituents, such as the red corpuscles, that enable it to carry different substances; and in part of the materials that are being carried. The latter, which include food and oxygen for the cells and wastes from the cells, may be classed as freight. Certain constituents in the blood destroy disease germs, and other constituents, by coagulating, close small leaks in the blood vessels. Although subject to rapid and continuous change, the blood is able—by reason of the balancing of materials added to and withdrawn from it—to remain about the same in quantity and composition.

Exercises.—1. Compare blood and water with reference to weight, density, color, odor, and complexity of composition.

2. Show by an outline the different constituents of the blood.

3. Compare the red and white corpuscles with reference to size, shape, number, origin, and function.

4. Name some use or purpose for each constituent of the blood.

5. What constituents of the blood may be regarded as freight and what as agents for carrying this freight?

6. After coagulation, what portions of the blood are found in the clot? What portions are found in the serum?

7. What purposes are served by water in the blood?

8. Show how the blood, though constantly changing, is kept about the same in quantity, density, and composition.

9. In the lungs the blood changes from a dark to a bright red color and in the tissues it changes back to dark red. What is the cause of these changes?

10. If the oxygen and hemoglobin formed a strong instead of a weak chemical union, could the hemoglobin then act as an oxygen carrier? Why?

11. What habits of living favor the development of corpuscles in the blood?

12. Why will keeping the skin clean and active improve the quality of one's blood?


*To demonstrate the Physical Properties of Blood* (Optional).—Since blood is needed in considerable quantity in the following experiments, it is best obtained from the butcher. To be sure of securing the blood in the manner desired, take to the butcher three good-sized bottles bearing labels as follows:

*1* Fill two thirds full. While the blood is cooling, stir rapidly with the hand or a bunch of switches to remove the clot.

*2* Fill two thirds full and set aside without shaking or stirring.

*3* Fill two thirds full and thoroughly mix with the liquid in the bottle.

Label 3 must be pasted on a bottle, having a tight-fitting stopper, which is filled one fifth full of a saturated solution of Epsom salts. The purpose of the salts is to prevent coagulation until the blood is diluted with water as in the experiments which follow.

*Experiments.*—1. Let some of the defibrinated blood (bottle 1) flow (not fall) on the surface of water in a glass vessel. Does it remain on the surface or sink to the bottom? What does the experiment show with reference to the relative weight of blood and water?

2. Fill a large test tube or a small bottle one fourth full of the defibrinated blood and thin it by adding an equal amount of water. Then place the hand over the mouth and shake until the blood is thoroughly mixed with the air. Compare with a portion of the blood not mixed with the air, noting any difference in color. What substance in the air has acted on the blood to change its color?

3. Fill three tumblers each two thirds full of water and set them in a warm place. Pour into one of the tumblers, and thoroughly mix with the water, two tablespoonfuls of the blood containing the Epsom salts. After an interval of half an hour add blood to the second tumbler in the same manner, and after another half hour add blood to the third. The water dilutes the salts so that coagulation is no longer prevented. Jar the vessel occasionally as coagulation proceeds; and if the clot is slow in forming, add a trace of some salt of calcium (calcium chloride). After the blood has been added to the last tumbler make a comparative study of all. Note that coagulation begins in all parts of the liquid at the same time and that, as the process goes on, the clot shrinks and is drawn toward the center.

4. Place a clot from one of the tumblers in experiment 3 in a large vessel of water. Thoroughly wash, adding fresh water, until a white, stringy solid remains. This substance is fibrin.

5. Examine the coagulated blood obtained from the butcher (bottle 2). Observe the dark central mass (the clot) surrounded by a clear liquid (the serum). Sketch the vessel and its contents, showing and naming the parts into which the blood separates by coagulation.

*To examine the Red Corpuscles.*—Blood for this purpose is easily obtained from the finger. With a handkerchief, wrap one of the fingers of the left hand from the knuckle down to the first joint. Bend this joint and give it a sharp prick with the point of a sterilized 'needle just above the root of the nail. Pressure applied to the under side of the finger will force plenty of blood through a very small opening. (To prevent any possibility of blood poisoning the needle should be sterilized. This may be done by dipping it in alcohol or by holding it for an instant in a hot flame. It is well also to wash the finger with soap and water, or with alcohol, before the operation.) Place a small drop of the blood in the middle of a glass slide, protect the same with a cover glass, and examine with a compound microscope. At least two specimens should be examined, one of which should be diluted with a little saliva or a physiological salt solution.(16) In the diluted specimen the red corpuscles appear as amber-colored, circular, disk-shaped bodies. In the undiluted specimen they show a decided tendency to arrange themselves in rows, resembling rows of coins. (Singly, the corpuscles do not appear red when highly magnified.)

A few white corpuscles may generally be found among the red ones in the undiluted specimen. These become separated by the formation of the red corpuscles into rows. They are easily recognized by their larger size and by their silvery appearance, due to the light shining through them.

*To examine White Corpuscles.*—Obtain from the butcher a small piece of the neck sweetbread of a calf. Press it between the fingers to squeeze out a whitish, semi-liquid substance. Dilute with physiological salt solution on a glass slide and examine with a compound microscope. Numerous white corpuscles of different kinds and sizes will be found. Make sketches.

*To prepare Models of Red Corpuscles.*—Several models of red corpuscles should be prepared for the use of the class. Clay and putty may be pressed into the form of red corpuscles and allowed to harden, and small models may be cut out of blackboard crayon. Excellent models can be molded from plaster of Paris as follows: Coat the inside of the lid of a baking powder can with oil or vaseline and fill it even full of a thick mixture of plaster of Paris and water. After the plaster has set, remove it from the lid and with a pocket-knife round off the edges and hollow out the sides until the general form of the corpuscle is obtained. The models may be colored red if it is desired to match the color as well as the form of the corpuscle.


A Carrier must move. To enable the blood to carry food and oxygen to the cells and waste materials from the cells, and also to distribute heat, it is necessary to keep it moving, or circulating, in all parts of the body. So closely related to the welfare of the body is the circulation(17) of the blood, that its stoppage for only a brief interval of time results in death.

*Discovery of the Circulation.*—The discovery of the circulation of the blood was made about 1616 by an English physician named Harvey. In 1619 he announced it in his public lectures and in 1628 he published a treatise in Latin on the circulation. The chief arguments advanced in support of his views were the presence of valves in the heart and veins, the continuous movement of the blood in the same direction through the blood vessels, and the fact that the blood comes from a cut artery in jets, or spurts, that correspond to the contractions of the heart.

No other single discovery with reference to the human body has proved of such great importance. A knowledge of the nature and purpose of the circulation was the necessary first step in understanding the plan of the body and the method of maintaining life, and physiology as a science dates from the time of Harvey's discovery.

*Organs of Circulation.*—The organs of circulation, or blood vessels, are of four kinds, named the heart, the arteries, the capillaries, and the veins. They serve as contrivances both for holding the blood and for keeping it in motion through the body. The heart, which is the chief organ for propelling the blood, acts as a force pump, while the arteries and veins serve as tubes for conveying the blood from place to place. Moreover, the blood vessels are so connected that the blood moves through them in a regular order, performing two well-defined circuits.

[Fig. 13]

Fig. 13—*Heart* in position in thoracic cavity. Dotted lines show positin of diaphragm and of margins of lungs.

*The Heart.*—The human heart, roughly speaking, is about the size of the clenched fist of the individual owner. It is situated very near the center of the thoracic cavity and is almost completely surrounded by the lungs. It is cone-shaped and is so suspended that the small end hangs downward, forward, and a little to the left. When from excitement, or other cause, one becomes conscious of the movements of the heart, these appear to be in the left portion of the chest, a fact which accounts for the erroneous impression that the heart is on the left side. The position of the heart in the cavity of the chest is shown in Fig. 13.

*The Pericardium.*—Surrounding the heart is a protective covering, called the pericardium. This consists of a closed membranous sac so arranged as to form a double covering around the heart. The heart does not lie inside of the pericardial sac, as seems at first glance to be the case, but its relation to this space is like that of the hand to the inside of an empty sack which is laid around it (Fig. 14). The inner layer of the pericardium is closely attached to the heart muscle, forming for it an outside covering. The outer layer hangs loosely around the heart and is continuous with the inner layer at the top. The outer layer also connects at certain places with the membranes surrounding the lungs and is attached below to the diaphragm. Between the two layers of the pericardium is secreted a liquid which prevents friction from the movements of the heart.

[Fig. 14]

Fig. 14—*Diagram of section of the pericardial sac*, heart removed. A. Place occupied by the heart. B. Space inside of pericardial sac. a. Inner layer of pericardium and outer lining of heart. b. Outer layer of pericardium. C. Covering of lung. D. Diaphragm.

*Cavities of the Heart.*—The heart is a hollow, muscular organ which has its interior divided by partitions into four distinct cavities. The main partition extends from top to bottom and divides the heart into two similar portions, named from their positions the right side and the left side. On each side are two cavities, the one being directly above the other. The upper cavities are called auricles and the lower ones ventricles. To distinguish these cavities further, they are named from their positions the right auricle and the left auricle, and the right ventricle and the left ventricle (Fig. 15). The auricles on each side communicate with the ventricles below; but after birth there is no communication between the cavities on the opposite sides of the heart. All the cavities of the heart are lined with a smooth, delicate membrane, called the endocardium.

[Fig. 15]

Fig. 15—*Diagram showing plan of the heart.* 1. Semilunar valves. 2. Tricuspid valve. 3. Mitral valve. 4. Right auricle. 5. Left auricle. 6. Right ventricle. 7. Left ventricle. 8. Chordae tendineae. 9. Inferior vena cava. 10. Superior vena cava. 11. Pulmonary artery. 12. Aorta. 13. Pulmonary veins.

*Valves of the Heart.*—Located at suitable places in the heart are four gate-like contrivances, called valves. The purpose of these is to give the blood a definite direction in its movements. They consist of tough, inelastic sheets of connective tissue, and are so placed that pressure on one side causes them to come together and shut up the passageway, while pressure on the opposite side causes them to open. A valve is found at the opening of each auricle into the ventricle, and at the opening of each ventricle into the artery with which it is connected.

The valve between the right auricle and the right ventricle is called the tricuspid valve. It is suspended from a thin ring of connective tissue which surrounds the opening, and its free margins extend into the ventricle (Fig. 16). It consists of three parts, as its name implies, which are thrown together in closing the opening. Joined to the free edges of this valve are many small, tendinous cords which connect at their lower ends with muscular pillars in the walls of the ventricle. These are known as the chordae tendineae, or heart tendons. Their purpose is to serve as valve stops, to prevent the valve from being thrown, by the force of the blood stream, back into the auricle.

The mitral, or bicuspid, valve is suspended around the opening between the left auricle and the left ventricle, with the free margins extending into the ventricle. It is exactly similar in structure and arrangement to the tricuspid valve, except that it is stronger and is composed of two parts instead of three.

[Fig. 16]

Fig. 16—*Right side of heart* dissected to show cavities and valves. B. Right semilunar valve. The tricuspid valve and the chordae tendineae shown in the ventricle.

The right semilunar valve is situated around the opening of the right ventricle into the pulmonary artery. It consists of three pocket-shaped strips of connective tissue which hang loosely from the walls when there is no pressure from above; but upon receiving pressure, the pockets fill and project into the opening, closing it completely (Fig. 16). The left semilunar valve is around the opening of the left ventricle into the aorta, and is similar in all respects to the right semilunar valve.

*Differences in the Parts of the Heart.*—Marked differences are found in the walls surrounding the different cavities of the heart. The walls of the ventricles are much thicker and stronger than those of the auricles, while the walls of the left ventricle are two or three times thicker than those of the right. A less marked but similar difference exists between the auricles and also between the valves on the two sides of the heart. These differences in structure are all accounted for by the work done by the different portions of the heart. The greater the work, the heavier the structures that perform the work.

[Fig. 17]

Fig. 17—*Diagram of the circulation*, showing in general the work done by each part of the heart. The right ventricle forces the blood through the lungs and into the left auricle. The left ventricle forces blood through all parts of the body and back to the auricle. The auricles force blood into the ventricles.

*Connection with Arteries and Veins.*—Though the heart is in communication with all parts of the circulatory system, it makes actual connection with only a few of the blood tubes. These enter the heart at its upper portion (Fig. 15), but connect with its different cavities as follows:

1. With the right auricle, the superior and the inferior venae cavae and the coronary veins. The superior vena cava receives blood from the head and the upper extremities; the inferior vena cava, from the trunk and the lower extremities; and the coronary veins, from the heart itself.

2. With the left auricle, the four pulmonary veins. These receive blood from the lungs and empty it into the left auricle.

3. With the right ventricle, the pulmonary artery. This receives blood from the heart and by its branches distributes it to all parts of the lungs.

4. With the left ventricle, the aorta. The aorta receives blood from the heart and through its branches delivers it to all parts of the body.

*How the Heart does its Work.*—The heart is a muscular pump(18) and does its work through the contracting and relaxing of its walls. During contraction the cavities are closed and the blood is forced out of them. During relaxation the cavities open and are refilled. The valves direct the flow of the blood, being so arranged as to keep it moving always in the same direction (Fig. 17).

The heart, however, is not a single or a simple pump, but consists in reality of four pumps which correspond to its different cavities. These connect with each other and with the blood vessels over the body in such a manner that each aids in the general movement of the blood.

[Fig. 18]

Fig. 18—Diagram illustrating the "cardiac cycle."

*Work of Auricles and Ventricles Compared.*—In the work of the heart the two auricles contract at the same time—their contraction being followed immediately by the contraction of both ventricles. After the contraction of the ventricles comes a period of rest, or relaxation, about equal in time to the period of contraction of both the auricles and the ventricles.(19) On account of the work which they perform, the auricles have been called the "feed pumps" of the heart; and the ventricles, the "force pumps."(20) It is the function of the auricles to collect the blood from the veins, to let this run slowly into the ventricles when both the auricles and ventricles are relaxed, and finally, by contracting, to force an excess of blood into the ventricles, thereby distending their walls. The ventricles, having in this way been fully charged by the auricles, now contract and force their contents into the large arteries.

*Sounds of the Heart.*—Two distinct sounds are given out by the heart as it pumps the blood. One of them is a dull and rather heavy sound, while the other is a short, sharp sound. The short sound follows quickly after the dull sound and the two are fairly imitated by the words "lubb, dup." While the cause of the first sound is not fully understood, most authorities believe it to be due to the contraction of the heart muscle and the sudden tension on the valve flaps. The second sound is due to the closing of the semilunar valves. These sounds are easily heard by placing an ear against the chest wall. They are of great value to the physician in determining the condition of the heart.

*Arteries and Veins.*—These form two systems of tubes which reach from the heart to all parts of the body. The arteries receive blood from the heart and distribute it to the capillaries. The veins receive the blood from the capillaries and return it to the heart. The arteries and veins are similar in structure, both having the form of tubes and both having three distinct layers, or coats, in their walls. The corresponding coats in the arteries and veins are made up of similar materials, as follows:

1. The inner coat consists of a delicate lining of flat cells resting upon a thin layer of connective tissue. The inner coat is continuous with the lining of the heart and provides a smooth surface over which the blood glides with little friction.

2. The middle coat consists mainly of non-striated, or involuntary, muscular fibers. This coat is quite thin in the veins, but in the arteries it is rather thick and strong.

3. The outer coat is made up of a variety of connective tissue and is also much thicker and stronger in the arteries than in the veins.

[Fig. 19]

Fig. 19—Artery dissected to show the coats.

Marked differences exist between the arteries and the veins, and these vessels are readily distinguished from each other. The walls of the arteries are much thicker and heavier than those of the veins (Fig. 19). As a result these tubes stand open when empty, whereas the veins collapse. The arteries also are highly elastic, while the veins are but slightly elastic. On the other hand, many of the veins contain valves, formed by folds in the inner coat (Fig. 20), while the arteries have no valves. The blood flows more rapidly through the arteries than through the veins, the difference being due to the fact that the system of veins has a greater capacity than the system of arteries.

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