2. Show by an outline the different const.i.tuents 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 const.i.tuent of the blood.

5. What const.i.tuents 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 quant.i.ty, 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?

PRACTICAL WORK

*To demonstrate the Physical Properties of Blood* (Optional).-Since blood is needed in considerable quant.i.ty 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 gla.s.s 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 ma.s.s (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 p.r.i.c.k 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 gla.s.s slide, protect the same with a cover gla.s.s, 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 gla.s.s 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 cla.s.s. 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.

CHAPTER V - THE CIRCULATION

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 s.p.a.ce 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._ s.p.a.ce 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 part.i.tions into four distinct cavities. The main part.i.tion 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.