THE CHEMISTRY OF BACTERIA. 103 



extent, if not wholly, the cause of this change. As a result 

 of gas production, vacuoles or spaces form in the mass. 

 The characteristic flavor and odor is due, as in the case of 

 butter, to bacterial products. Abnormal fermentations in 

 a cheese may give rise to poisonous products, or to marked 

 alteration in the appearance of the cheese. 



Butyric acid fermentation. This rather common fermen- 

 tation is usually the result of the action of anaerobic bac- 

 teria. A considerable number of obligative anaerobes have 

 been described as producers of butyric acid. The patho- 

 genic organisms of this class may form butyric acid, even in 

 the animal body. A number of aerobic bacteria can like- 

 wise give rise to butyric acid. 



Many of the anaerobes mentioned, give a granulose re- 

 action on contact with iodine. They are usually motile, 

 and in those species which develop spores, there is always 

 a corresponding enlargement of the cell. Hence, either the 

 clostridium, or drum-stick forms are met with in such cases. 



In this, as in other fermentations, various additional 

 products are encountered. Among these may be mentioned, 

 butyl alcohol, acetic and carbonic acids, hydrogen, etc. 

 The material acted upon may be a carbohydrate, such as 

 glucose, or it may be a protein, or a fat. It is evident that 

 butyric, like lactic acid, is a very common product in the 

 decomposition of organic matter. The transformation of 

 glucose into butyric acid is usually represented by the 

 equation: 



C 6 H 12 6 - C 4 H 8 2 + 2 C0 2 + 2 H 2 . 



Glucose. Butyric acid. 



Butyric acid is ordinarily prepared by allowing milk, to 

 which calcium carbonate has been added, to undergo lactic 

 acid fermentation. The lactic acid unites with the lime to 

 form calcium lactate. Eventually, this salt is acted upon 

 by other organisms and butyric acid forms. 



