PRODUCTS OF MICROBIAL ACTIVITIES 239 



Some of the acids can also undergo an anaerobic fermentation. 

 This is possible only with hydroxy-acids. The fermentation of the 

 calcium salt of tartaric acid was the first anaerobic fermentation 

 observed by Pasteur, and the fermentation of lactic acid to butyric 

 acid has a reputation for its chemical peculiarity. A compound with 

 four carbon atoms is formed from a compound with only three carbons, 

 a very unusual thing in fermentation. 



FATS. The decomposition of fats is comparatively simple. All fats 

 are glycerides of organic acids, and if they are attacked at all by micro- 

 organisms, they are first split into glycerin and free acid. 



H 2 C - O - CO - Ci 5 H 3 i HOH H 2 COH HO 2 C-C 15 H 31 

 HC - O - CO - Ci 5 H 3 i + HOH = HCOH + HO 2 C-Ci 5 H 31 



H 2 C - O - CO - C 15 H 31 HOH H 2 COH HO 2 C-Ci 5 H 31 



Fat Water Glycerin Acid 



This brings about the liberation 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 little 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 limited, 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, 



