242 NUTRITION AND METABOLISM 



the nitrogen-containing fragments of the protein molecule are con- 

 cerned. That ammonia is formed by many microorganisms, is well 

 known. In some decaying proteins, e.g., in old Camembert cheese, 

 ammonia can be very easily detected by the smell. As all proteins 

 conta'n many amino-groups as well as ac'd-amid groups, it is easily 

 understood how the ammonia originates through the hydrolysis of pro- 

 tein. In the complete oxidation of proteins the nitrogen is always left 

 as NH 3 or (NH 4 ) 2 CO 3 , respectively, never, so far as known, in any other 

 form. No bacterium is known to produce urea, as most of the higher 

 animals do. 



In the products of protein degradation mentioned above only 

 those compounds have been considered which contain nitrogen. It is 

 quite evident, however, that in the cleavage of the large and complex 

 protein molecules, certain parts of the molecule will contain no nitrogen. 

 Many organic acids, like acetic, butyric, capronic, benzoic and phenyl- 

 acetic acids are quite generally found among the products of putre- 

 faction. Alcohols too, especially benzene derivatives like phenol and 

 cresol, are not unusual. Gas is often formed in putrefaction, especially 

 carbon dioxide and hydrogen; occasionally these gases are mixed with 

 traces of nitrogen and methane. 



Many protein compounds contain, besides the organic elements, 

 larger or smaller amounts of phosphorus and sulphur. The phos- 

 phorus compounds may be changed to phosphine (PH 3 ), which is a gas 

 of a strong disagreeable garlic odor. Generally, however, the phos- 

 phorus of protein after its degradation is found as phosphoric acid 

 (H 3 PO 4 ). Very little is known about the phosphorus of organic 

 compounds and the changes it may undergo in the putrefactive process. 



The sulphur of proteins is commonly changed to hydrogen sulphide 

 (H2S). Some microorganisms are able to form mercaptan (CH 3 SH), 

 a compound of very foul penetrating odor. 



After this enumeration of the products, the main types may be 

 considered briefly; since much less work has been done on protein 

 decomposition than on carbohydrate decomposition, the groups are 

 not so well defined. We might consider the following types: 



Complete Oxidation. This is brought about by many molds, by 

 yeasts if they depend upon proteins only, and by many bacteria, of 

 which the large, aerobic spore-forming rods, such as B. mycoides, are 

 the main representatives. The products of oxidation are CO2, 



