PRODUCTS OF METABOLISM 1 69 



This brings about the hberation of three molecules of free acid from 

 a neutral fat molecule. It is customary to test for the splitting of fat by 

 determining its acidity. The glycerin is readily used up by the micro- 

 organisms, while the fatty acids are oxidized but very slowly. 



The number of organisms which can attack fat is quite small. 

 Most molds can destroy it; one torula has been found in butter which 

 attacks it, and perhaps a dozen species of bacteria will do the same, 

 among them B. fluorescens and B. prodigiosus, which cause occasionally 

 the rancidity of butter. 



Products from Nitrogenous Compounds 



On account of the complexity of the protein molecule, the products 

 of protein decomposition by microorganisms are Httle known. Some 

 products are conspicuous through their odor, others can be told by cer- 

 tain color reactions, but as we cannot, at the present, give the structural 

 formula of proteins, there is no possibility of stating protein decomposi- 

 tions in equations similar to those of carbohydrate fermentations. 

 The discussion must be hmited, for this reason, to the enumeration of the 

 most important products, and to the general types of decomposition. 



As in the carbohydrates, soluble compounds are more easily de- 

 composed than the insoluble. The keratin bodies of hair, epidermis 

 and horn are slowly attacked by a very few organisms. Gelatin, 

 - casein and serum albumin are more readily decomposed, though their 

 solubiUty is quite limited. Peptones wjbich are readily soluble are 

 used by the vast majority of microorganisms. Of interest in this con- 

 nection is the fact that the fresh white of egg is poisonous to most bac- 

 teria, and fresh blood and animal tissues as well as freshly drawn milk 

 have also germicidal properties which are lost by heating or upon 

 standing. 



Protein bodies are as numerous as plants and animals. Each 

 species of organism seems to have its particular protein which differs 

 from that of other species. With the more highly developed organisms, 

 there are several distinctly different proteins found in the same individ- 

 ual in different parts of the body. The constituents, carbon, oxygen, 

 hydrogen, nitrogen, and sometimes sulphur and phosphorus can be 

 determined in their relative amounts without, however, furnishing any 

 knowledge of the structure of the molecule. The molecular weight of 



