BIOLOGY OF BACTERIA. 49 



times not. The production of coagulation in milk is not 

 always associated with acid-production, but with the pro- 

 duction of a curdling ferment similar to that belonging 

 to the gastric juice. There seems to be no real specific 

 micro-organism for the lactic-acid fermentation, although 

 the Bacillus acidi lactici seems to be the most powerful 

 generator of the acid. There may also be several bac- 

 teria which produce the acetic fermentation, though it is 

 generally attributed to a special common form, the Myco- 

 derma aceti or Bacillus aceticus. The butyric fermenta- 

 tion is generally due to the Bacillus butyricus, though it 

 also may be caused by other bacilli, the one named sim- 

 ply being the most common. (For an exact description 

 of the chemistry of the fermentations reference must be 

 made to text-books upon that subject, as their considera- 

 tion here would occupy too much space.) 



2. Putrefaction. This process is in many respects sim- 

 ilar to the preceding, except that instead of occurring in 

 carbohydrates it takes place in nitrogenous bodies. The 

 first step seems to be the transformation of the albumins 

 into peptones, then the splitting up of the peptones into 

 a large number of gases, acids, bases, and salts. In the 

 process the innocuous albumins are frequently changed to 

 toxalbumins, and sometimes to distinct animal alkaloids 

 known as ptomaines. Vaughan and Novy declare the 

 term "animal alkaloid" to be a misnomer, as ptomaines 

 are sometimes produced from vegetable substances in 

 the process of decomposition ; they suggest the term 

 u putrefactive alkaloids" as preferable. The definition 

 of a ptomaine given by these observers is u a chemical 

 compound, basic in character, formed by the action of 

 bacteria on organic matter." The chemistry of these 

 bodies is very complex, and for a satisfactory description 

 of them Vaughan and Novy's book 1 is brief and excel- 

 lent. Among the ptomaines the following appear to 

 be important: Methylamin (CH 3 NH 2 ), the simplest or- 

 ganic base formed in the process of putrefaction; dime- 



1 Ptomaines and Leucomalnes. 

 4 



