A few white corpuscles may generally be found among the red ones in the undiluted specimen. These become separated by the formation[pg 039] 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.
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 [pg 041]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.