204 HUMAN PHYSIOLOGY 



rest of the gas must be equally distributed through the 

 blood, and thus the amount of blood may be deduced. 



By this method they conclude that the volume of the 

 blood is about ?\ih of the weight of the body. 



VII. Distribution of the Blood. 



Roughly speaking, the blood is distributed somewhat as 

 follows : 



Heart, lungs, large vessels J 



Muscles ....... J 



Liver 



Other organs J 



YIII. Fate of the Blood Constituents. 



The water of the blood, constantly renewed from outside, 

 is constantly got rid of by the kidneys, skin, lungs, and 

 bowels. 



About the fate of the proteids we know nothing. They 

 must be used up in the construction of the tissues, but 

 experimental evidence of this is wanting. 



The glucose and fat are undoubtedly used up in the 

 tissues. 



The urea and waste products are excreted by the kidneys. 



The fate of the salts is not fully worked out. The chlorides 

 are partly excreted by the kidneys and are partly split up 

 to form the hydrochloric acid required for stomach diges- 

 tion. The phosphates and sulphates are excreted in the 

 urine, but whether they are also used in the tissues is not 

 known. 



The leucocytes break down in the body but when and 

 how we do not know. We shall afterwards find that they 

 are greatly increased in number after a meal of proteids, and, 

 since the increase is transitory, lasting only for a few hours, 

 they are probably rapidly broken down, possibly to feed the 

 tissues. It would thus seem that a leucocyte lives in the 

 blood only for a short time. 



The erythrocytes also break down. How long they live 

 is not known. It is found, after injecting blood, that the 



