286 FERMENTATIONS IN MILK 



In addition to the indirect butyric acid fermentation 

 of milk sugar, direct fermentation of this and other sugars 

 without the preliminary change into lactic acid can be 

 carried out by several organisms ; other bacteria ar.e 

 known which produce butyric acid from starch, citric, 

 malic, and other acids, and from glycerine. 



It is usual to limit the term butyric acid fermentation 

 more particularly to the production of this acid from 

 carbohydrates and glycerine. Most of the organisms 

 possessing this power are anaerobic bacilli, which in 

 a vegetative state store up granulose, a kind of carbo- 

 hydrate giving a blue or violet colour with iodine, like 

 that given by starch. They form highly resistant 

 spores, which may be heated to the temperature of 

 boiling water without being destroyed. These often 

 appear in the middle of the bacterial cell, and when 

 fully developed bulge out the walls of the latter into the 

 form of a spindle ; a bacterial cell of this shape is usually 

 termed a Clostridium. 



Besides the above typical butyric acid fermentations 

 in which a carbohydrate is broken down, with the forma- 

 tion of butyric acid as a chief product, many fermentations 

 are known in which butyric acid in larger or smaller 

 amounts arises in the decomposition of proteins, the 

 organisms concerned belonging mainly to the putrefactive 

 class, most of them being closely allied to Bs. vulgatus. 



Butyric Acid Bacteria. i. Great uncertainty exists 

 in regard to the relationship of the butyric acid organisms 

 described by many different writers ; Pasteur's vibrion 

 butyrique, and Van Tieghem's Bacillus Amylobacter, were 

 considered by Prazmowski the same as his Clostridium 

 butyricum. It is not feasible here to give an account of 

 the various forms which have been described. Most of 



