270 



THE BLOOD. 



Temperature of Blood. The temperature of the blood varies 

 greatly in the different parts of the circulatory apparatus. The 

 mean temperature may be stated as 39 C.; that of the superior 

 vena cava, 36.78 C.; the right side of the heart, 38.8 C.; the 

 left side of the heart, 38.6 C.; the aorta, 38.7 C.; the portal 

 vein, 39.9 C.; the hepatic vein, 41.3 C. The temperature of 

 the blood in the hepatic vein is the highest in the body, and it 

 varies from 39.5 C. at the beginning of digestion to 41.3 C. at 

 the time when the process is most active. The blood in the right 

 side of the heart is made warmer by its proximity to the liver, 

 while in its circulation through the lungs it loses heat, and is there- 

 fore cooler in the left side of the heart. In the portions of the 



body exposed to the air, as in 

 the skin, the temperature of 

 the blood may be doubtless as 

 low as 36.5 C. 



Distribution of Blood. 

 The distribution of blood in 

 the body is as follows : In the 

 heart, lungs, and great blood- 

 vessels, one-fourth; in the 

 skeletal muscles, one-fourth ; 

 in the liver, one-fourth ; in 

 the rest of the body, one- 

 fourth. 



Microscopic Structure 

 of the Blood. When ex- 

 amined by the microscope the 

 blood is seen to be composed 

 of corpuscles suspended in a 

 fluid, the plasma or liquor 

 sanguinis. 



Blood-corpuscles. By 

 means of a hematocrit (Fig. 

 143) the average percentage 

 of corpuscles in human blood 



FIG. 143. Hematocrit. has been found to be about 48 



for males, and 43.3 for females, 



while for children of from six to thirteen years it is 45. In mak- 

 ing this determination the blood is mixed with a measured quan- 

 tity of a 2J per cent, solution of potassium bichromate, and then 

 placed in a tube which is revolved very rapidly, or, as it is 

 expressed, centrifugalized. The corpuscles accumulate at the bot- 

 tom of the tube, while the plasma remains above them, and the 

 volume can be determined by simply reading the scale. 



The corpuscles of the blood are of three varieties : (1) Red 

 corpuscles ; (2) colorless corpuscles ; and (3) plaques. 



Red corpuscles in human blood are circular, biconcave, non- 



