226 HITCHCOCK'S ANATOMY 



tremities, where the arterial blood, by its affinity for the 

 healthy tissues, forces along that which is already surcharged 

 with carbonic acid into the systemic veins. 



397. Forces of the whole Circulation. — The forces, then, 

 which propel the blood through the whole system may be thus 

 briefly summed up : 



1. Contraction of the heart. 



2. Elasticity of the arteries. 



3. Capillary force. 



4. Muscular pressure. 



5. Act of inspiration. 



6. Arterialization of the blood. 



398. Course of the Blood through the Body. — As al- 

 ready mentioned, the ventricles are the propelling and the 

 auricles the receiving cavities. Hence, in tracing the course 

 of the blood through the body, beginning with the left ven- 

 tricle, we find the current passing through the aorta and ar- 

 teries to all parts of the body except the lungs. As soon as 

 it has gone through the capillaries it returns to the right au- 

 ricle by the different veins, from which cavity it passes to the 

 right ventricle, and thence to the lungs. After it has received 

 its due supply of oxygen, it is received by the left auricle, 

 from which it passes again to the whole system. The parts 

 of this circle and their order are as follows : left ventricle, ar- 

 teries, capillaries, veins, right auricle, right ventricle, lungs, 

 and left auricle. Thus we see that the whole circulation in 

 man and all mammalia follows through the body a course 

 represented by the figure 8. 



399. Relative Time Occupied by Contraction of Au- 

 ricles and Ventricles —The diastole or dilatation of auricles 

 and ventricles occupies a longer period of time than the cor- 

 responding systole, or contraction. If we divide the whole 



397. Give a synopsis of the circulatory forces. 398. Give the course taken by the 

 blood as it circulates through the body. By what figure may it be represented? 399. 

 What is the systole and diastole of the heart ? 



