206 



Human Physiology. 



extremities, and wherever there is a gland to act or a tissue 

 to be nourished ; returning from every portion through the 

 veins to the right side of the heart. 



This circulation goes on with great rapidity. The heart beats 

 4,200 times an hour, day and night. At each beat two and a 

 half ounces are thrown into the arteries, which is at the rate of 

 six hundred and fifty-six pounds an hour, or seven and three- 

 fourth tons a-day. A quantity equal to all the blood in the 

 body passes through the heart every three minutes. 



Fig. 48. 



DISTRIBUTION OF 

 CAPILLARY BLOOD- 

 VESSELS IN THE SKIN 

 OF THE FINGER. 



Fig. 49. INJECTED VEINS FROM 

 COAT OF INTESTINE. 



The arteries terminate in minute tubes, called capillaries, 

 which carry the blood into very extensive ramifications in the 

 muscles, glands, brain in short into every tissue. Fig. 48 

 shows the distribution of capillaries in the skin of the finger, 

 where there is a similar distribution of the nerves of sensa- 

 tion. The whole skin is pervaded with these minute blood- 

 vessels, which are thicker in the more sensitive portions. 

 Most are so small as only to carry white globules; in rosy 



