172 NUTRITION AND METABOLISM 



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 (PH3), which is a. gas 

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

 phprus of protein after its degradation is found as phosphoric acid 

 (H3PO4). 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 (CH3SH), 

 a compound of very foul penetrating odor. 



After this enumeration of the products, the main t3^es 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, H2O, 

 NH3 and H2SO4. The nitrogen is never changed to any oxidation 

 product, but is found as NH3, while the sulphur is oxidized. 



Incomplete oxidation is caused by other bacteria, and perhaps molds 

 and yeasts. Quite a large number of organisms live on sugar-free 

 media if they have oxygen, but they do not oxidize their food com- 

 pletely. We can distinguish at least three different groups of micro- 

 organisms here. 



B. proteus is the collective name for a number of closely related 

 forms which belong to the most common organisms found on decaying 

 organic matter, especially when protein is abundant. They produce 

 leucin, tyrosin and tryptophane, but no skatol, or phenol. Indol 

 and hydrogen sulphide are formed in certain media. Less important, 

 but also very common are the pigment-forming rods among which B. 

 fluorescens, B. prodigiosus, Ps. pyocyanea are the best-known repre- 

 sentatives. Their metabolism is a little different; amins and ammonia 

 are formed, while hydrogen sulphide, phenol and indol are absent. 



