THE CHEMISTRY OF THE ANIMAL BODY 155 



The nitrogenous matter shows the least variation, while 



the water and fat are more or less complementary to each 



other — i.e.y as the one increases the other decreases. The 



ash is dependent chiefly upon the proportion of bono present. 



The chief parts of an animal's body are : 



1 . Blood. 4. Fatty tissue. 



2. Bones, 5. Connective tissue. 



3. Muscular tissue. 



Blood consists of a colourless liquid — " plasma " — holding, in 

 suspension, enormous numbers of small solid particles — the red 

 and white corpuscles. When taken from an animal, the plasma 

 quickly deposits one of its nitrogenous constituents— ^5ri?i — 

 which, entangling the corpuscles, causes them to separate as a 

 clot from the yellowish liquid — the serum. Blood plasma is 

 thus the liquid portion of fresh blood, blood serum the liquid 

 portion after clotting. The latter differs from the former by 

 having lost its fibrin, ov fibrinogen^ as it is now called, and a 

 portion of its lime, magnesia, and phosphoric acid. Blood 

 serum contains about 9 per cent, of total solids, of which 

 7*5 are albuminoid. Its ash amounts to about 8 5 per 

 cent., and consists chiefly of common salt, with small quan- 

 tities of potash, lime, and magnesia. 



The clot of blood consists of red and colourless corpuscles 

 entangled in a network of fibrin. The red corpuscles consist 

 of circular, biconcave discs, though their shape and size vary 

 in different animals. They are largest in reptiles. In birds, 

 fishes, and in the camel they are elliptical and biconvex. 

 In man, the average diameter of a blood corpuscle is "OC? '^^m. 

 (about u-jV?y ^^ ^^ inch), and its thickness about '0019 mm. 

 (itItji^ of an inch). When blood corpuscles are treated with 

 water, ether, or other solvents they lose their colouring-matter 

 and leave a nitrogenous residue, which retains the shape of 

 the original corpuscles. 



The colour of blood is due to hcemoglobin and oxyhcemoglohin. 

 These are extremely complex in chemical constitution, and 



