CHEMICAL BASIS OF THE ANIMAL BODY. 5 



possess or promise to possess physiological interest. The physiological 

 function of any substance must depend ultimately on its molecular 

 (including its chemical) nature; and though at present our chemical 

 knowledge of the constituents of an animal body gives us but little 

 insight into their physiological properties, it cannot be doubted that 

 such chemical information as is attainable is a necessary preliminary to 

 all physiological study. 



PROTEIDS \ 



. 

 These form the principal solids of the muscular, nervous, and gland- 



ular tissues, of the serum of blood, of serous fluids, and of lymph. In 

 a healthy condition, sweat, tears, bile and urine contain mere traces, if 

 any, of proteids. Their general percentage composition may be taken 

 as lying within the following limits : 



C 50-0 to 55-0 ......... ... 50-0 to 55-0 



H 6-9 7-3 ............ 6-8 7-3 



N 15-0 18-0 ............ 15-4 18-2 



O 20-0 23.5 ............ 22-8 24-1 



S 0-3 2-0 ............ 0-4 5-0 



(Hoppe-Seyler 2 . ) (Drechsel. ) 



The composition of the true proteids lies so constantly within the 

 above limits that conclusions as to the proteid nature of any substance 

 whose purity is assured may be drawn with safety from the results of 

 its ultimate analysis. This is important in cases where a substance is 

 with difficulty, if at all, obtained in a condition such that it yields none 

 of the reactions characteristic of proteids. Kiihne and Chittenden's 

 analyses 3 of peptones freed from albumoses, which they quote with 

 considerable reserve, alone show a percentage composition lying appre- 

 ciably outside the above limits. 



In addition to the above constituents, proteids ordinarily leave on ignition a 

 variable quantity of ash. In the case of egg-albumin the principal constituents of 

 the ash are chlorides of sodium and potassium, the latter exceeding the former in 

 amount. The remainder consists of sodium and potassium, in combination with 

 phosphoric, sulphuric, and carbonic acids, and very small quantities of calcium, 

 magnesium and iron, in union with the same acids. There may be also a trace of 



1 The chemistry of proteids and allied substances, together with a compendious 

 literature of the subject, is very fully treated and recorded in Drechsel's article 

 "Eiweisskorper" in Ladenburg's Handworterbuch der Chemie, Bd. in. (1885), S. 534, 

 and in Beilstein's Handbuch der organischen Chemie, Bd. in. (1882-90), S. 1258. 



2 Hdbch. d. phys. path. chem. Anal., Auf. 5 (1883), S. 258. 



3 Zt. f. Biol. Bd. xxn. (1886), S. 452. 



