268 THE HUMAN BODY 



other salts, and extractives of which the most constant are urea, 

 creatinine, uric acid, and grape-sugar; (2) red corpuscles, contain- 

 ing rather more than half their weight of water, the remainder 

 being mainly hemoglobin, other proteins, and potash salts; (3) 

 white corpuscles, consisting of water, various proteins, glycogen, 

 and potash salts; (4) the platelets; (5) gases, partly dissolved in 

 the plasma or combined with its sodium salts, and partly com- 

 bined (oxygen) with the hemoglobin of the red corpuscles. 



Quantity of Blood. The total amount of blood in the Body is 

 difficult of accurate determination. It is about ^ of the whole 

 weight of the Body, so the quantity in a man weighing 75 kilos 

 (165 Ibs.) is about 5.8 kilos (12.7 Ibs.). Of this at any given 

 moment about one-fourth would be found in the heart, lungs, and 

 larger blood-vessels; and equal quantities in the vessels of the 

 liver, and in those of the muscles which move the skeleton; while 

 the remaining fourth is distributed among the remaining parts 

 of the Body. 



Blood of Other Animals. In all animals with blood the white 

 corpuscles are pretty much alike, but the red corpuscles, which 

 with rare exceptions are found only in Vertebrates, vary con- 

 siderably. In all the classes of the mammalia they are circular 

 biconcave disks, with the exception of the camel tribe, in which 

 they are oval. They vary in diameter from 0.02 mm. (^ inch) 

 (musk deer) to 0.011 mm. (^5 inch) (elephant). In the dog 

 they are nearly the same size as those of man. In no mammals 

 do the fully-developed red corpuscles possess a nucleus. In all 

 other vertebrate classes the red corpuscles possess a central 

 nucleus, and are oval slightly biconvex disks, except in a few 

 fishes in which they are circular. They are largest of all in the 

 amphibia. Those of the frog are 0.022 mm. (^ inch) long and 

 0.015 mm. (^ inch) broad. 



The blood of certain crustaceans contains instead of hemo- 

 globin a substance of similar physiological action, hemocyanin, 

 which is blue instead of red, and contains copper in place of iron. 



Histology and Chemistry of Lymph. Pure lymph is a color- 

 less watery -looking liquid; examined with a microscope it is seen 

 to contain numerous white corpuscles closely resembling those of 

 the blood, and no doubt many are leucocytes which have mi" 

 grated. These lymph-corpuscles or leucocytes have, however, 



