PRODUCTS OF METABOLISM. 1 17 



mentioned products will be readily oxidized to simpler compounds and 

 finally to carbon dioxide, water, ammonia; the ammonia may be oxidized 

 further to nitrous or nitric acid, as has been mentioned already in several 

 chapters. The final oxidation of the carbon compounds is the complete 

 combustion, accomplished at once, or in successive steps by different 

 organisms. Hydrogen sulphide is oxidized to sulphur or sulphuric acid. 

 Thus we obtain as the final products of protein degradation carbon 

 dioxide, water, ammonia, nitrates, nitrogen, hydrogen, hydrogen sulphide, 

 sulphuric acid, phosphoric acid. The protein is completely mineralized. 

 UREA, URIC ACID, HIPPURIC ACID are the products of protein digestion 

 in the animal body. Urea is a normal product in the urine of many 

 animals, especially the carnivora, while hippuric acid is produced 

 mainly by herbivora and uric acid is one of the main constituents in the 

 excreta of birds and snakes. The fermentation of urea to ammonium 

 carbonate has been discussed extensively in the chapter on metabolism, 

 page 85. It is a simple hydrolysis. 



CO(NH 2 ) 2 + 2 H 2 0= C0 3 (NH 4 ) 2 . 



Only one group of bacteria, the urea bacteria, can perform this change, 

 a few molds are also said to cause this fermentation. Hippuric acid is of 

 much more complex nature, benzoyl-amino-acetic acid. It is probably 

 split up by bacteria into benzoic acid and amino-acetic acid 



C 6 H 5 CO. NH CH 2 COOH +HOH=C e H 6 COOH+NH 3 CH 2 COOH 



Hippuric acid Benzoic acid Amino-acetic acid 



Uric acid, also a complex organic body, can be oxidized through the 

 agency of bacteria by several processes which yield ammonium carbonate 

 and carbon dioxide. Often urea is an intermediate product forming in 

 the following manner: 



Uric acid Urea 



The decomposition of these three compounds takes place continuously 

 in manure piles and in sewage. The final result is, as with proteins, a 

 complete mineralization. 



PRODUCTS FROM MINERAL COMPOUNDS. 



Minerals are used by microorganisms for cell construction almost 

 exclusively; consequently, they do not leave the living cell like fermenta- 

 tion products. But a few organisms can actually decompose mineral 



