Chemical Changes in Animal Organism. 279 



precipitated by dilution with water. It is of interest to 

 note that the two chief phospho-proteins, caseinogen and 

 vitellin, are constituents of the foods of young animals or 

 developing embryos. 



(3) THE URINE AND FAECES. 



The urine contains a large variety of salts and organic 

 substances, but the most interesting constituents are the 

 nitroenous substances. The chief of these is urea, or 



carbamide, 



ide, OC<^ 2 . Small amounts of ammonia are 



X.N Ll^ 



almost invariably found in urine. The quantity can be 

 estimated by making a known amount of urine alkaline 

 with sodium carbonate, and drawing a current of air 

 through the liquid warmed to about 40. After passing 

 the urine, the air is bubbled through a flask containing 

 a measured quantity of standard acid solution, which is 

 titrated with standard alkali at the end of the experiment. 

 From the result of this titration the amount of ammonia 

 (or ammonium salts) in the urine can be calculated. The 

 urea can be estimated in the urine by drawing air through 

 a measured amount of the liquid, heated to 40, to which 

 some powdered Soya bean has been added. This contains 

 a ferment capable of decomposing urea into ammonia and 

 carbon dioxide 



CO(NH 2 ) 2 + H 2 = H 2 C0 3 + 2NH 3 



The ammonia is drawn by the air through standard acid. 

 After a time sodium carbonate is added, and the air current 

 is continued till all the ammonia is driven off. From the 

 amount of ammonia absorbed by the standard acid the 

 quantity of urea present can be calculated, after allowance 

 has been made for the ammonia pre-existing as such, and 

 determined by the method already mentioned. Uric acid 



