Reproduced by courtesy of Messrs. F. Davidson &* Co. 

 RED BLOOD CORPUSCLES OF MAN 



Each cell or corpuscle is a circular disk, on an average about ggfoj 

 of an inch in diameter, and about one-fourth of that in thickness. 

 More than a million will lie on a square inch. The broad faces 

 are not flat, but slightly concave; so the corpuscles are thinner in 

 the middle than at the margin. When seen edge-on they look 

 like rods. Their colour is faint yellowish- red, due to the pigment 

 hemoglobin, which has a great affinity for oxygen. The mam- 

 malian red blood corpuscle does not show any nucleus except in 

 the early stages of development. The white blood corpuscles are 

 larger, nucleated, and irregular. The red blood corpuscles are 

 mostly made in the marrow of the bones and mostly destroyed 

 in the liver and spleen. 



DIASTOLE 



SYSTOLE 



DIAGRAM ILLUSTRATING THE VALVES OF THE HEART 



During the period of contraction (systole) of either of the ven- 

 tricles the valves which guard the opening of the big artery are 

 open, whilst the valves at the gateway between auricle and ven- 

 tricle are closed, thus preventing blood from being forced back 

 into the auricle. During the period of relaxation (diastole) of 

 the ventricle, the valves of the artery are closed and those be- 

 tween auricle and ventricle are open, allowing blood to flow freely 

 from auricle to ventricle, but preventing back-flow from the 

 artery. 



Both auricles contract at the same time. Then both ventricles 

 contract simultaneously. Then there is a short pause. Each 

 complete cycle, including the pause, is a "beat "; and in a healthy 

 adult the heart beats about seventy-two times in a minute. 



TISSUES 



OF THE , 

 > BODY / 



DIAGRAM OF THE CIRCULATION 



OF THE BLOOD THROUGH THE 



BODY 



Seventy-two times a minute the 

 heart beats; that is to say, its muscu- 

 lar walls contract. Each half of the 

 heart consists of two chambers: the 

 auricle, which receives blood from the 

 big veins, and the ventricle, which re- 

 ceives blood from the auricle and 

 pumps it into the big arteries. Be- 

 tween the right and left sides of the 

 heart there is no direct communica- 

 tion. Aerated blood is collected 

 from the capillaries of the lungs and 

 conveyed by the pulmonary veins to 

 the left auricle, whence it passes to 

 the left ventricle. Thence it is 

 pumped into the great artery, the 

 aorta, whose branches distribute it to 

 every part of the body. Having given 

 up much of its oxygen and nourish- 

 ment to the tissues needing them, the 

 blood is collected and conveyed by 

 veins to the right auricle. From there 

 it passes to the right ventricle, which 

 forces it through the pulmonary 

 arteries to the lungs where it is 

 aerated and again travels to the left 

 side of the heart, ready to be again 

 circulated. It will be noted that 

 arteries are blood-vessels leaving the 

 heart, while veins are blood-vessels 

 returning to the heart. The arteries 

 carry pure blood, except in the case of 

 the pulmonary arteries to the lungs. 

 The veins carry impure blood, except 

 in the case of the pulmonary veins 

 from the lungs. 



