• BLOOD 503 



reduce the volume in circulation to such an extent that the 

 supply of oxygen to the tissues is seriously interfered with. 



VIII. Distribution of the Blood. y 



Roughly speaking, the blood is distributed somewhat as 

 follows : — 



Heart, lungs, large vessels ... J 



Muscles ...... ^ 



Liver ....... ^ 



Other organs ..... ^ 



IX. Fate of the Blood Constituents. 



A. Of the Plasma. — The water of the blood is got rid of by 

 the kidneys, skin, lungs, and bowels. 



About the fate of the proteins we know nothing. 



The glucose and fat are undoubtedly used up in the 

 tissues. 



The urea and waste products are excreted by the kidneys. 



As already indicated, the salts of the blood play the triple 

 part (1) of supplying the tissues with the necessary cations; 

 (2) of maintaining the osmotic pressure of the blood ; (3) 

 of regulating the Cjj of the blood. Their due proportion is 

 maintained chiefly by the action of the kidneys, which 

 respond at once to any change in the C^ of the blood by 

 eliminating the excess of anions or of cations. 



B. Of the Cells. — (1) The leucocytes break down in the 

 body — but when and how is not known. They are greatly 

 increased in number after a meal of proteins (digestion 

 leucocytosis, p. 348), and, since the increase lasts only for a 

 few hours, they are probably rapidly broken down, possibly to 

 liberate amino-acids. But it is also possible that they may 

 return to the bone-marrow and lymph tissue, from which 

 they emerged during digestion. 



(2) The erythrocytes also break down. How long they 

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

 from another animal of the same species, the original number 

 of corpuscles is not reached for about a fortnight ; and hence 

 it has been concluded that the corpuscles live for that 



