^4 BACTERIOLOGY. 



changes largely, if not wholly, by means of the soluble fer- 

 ments or enzymes which they elaborate. 



Diverse fermentations result, depending upon the kind 

 of organism at work, and, the material that is acted upon. 

 It has been customary to restrict the term fermentation to 

 those phenomena where carbohydrates undergo cleavage. 

 The word fermentation (meaning, to boil) was originally ap- 

 plied to those changes which were accompanied by the ac- 

 tive evolution of gas, in which case the liquid appeared to 

 be boiling. This conception must be enlarged to accord 

 with the action of bacteria in general. It matters not 

 whether the substance that is acted upon is a carbohydrate, 

 fat, or protein; whether gaseous products are, or are not 

 evolved; the change, if due to a micro-organism, is one of 

 fermentation. 



In the decomposition of albuminous substances dis- 

 agreeable products are evolved. Putrefaction can, conse- 

 quently, be designated as putrid fermentation. The chem- 

 ical composition of the protein molecule accounts for the 

 different products thus obtained as compared with those 

 which result in the decomposition of carbohydrates. The 

 latter contain only C, H and O, and, on fermentation, yield 

 diverse alcohols and acids which are not disagreeable. On 

 the other hand, the protein molecule usually contains in ad- 

 dition to the elements mentioned, N, S and P. Hence, in 

 putrefaction various N compounds form such as ammonia, 

 amines, indol, skatol, etc., which possess a more or less of- 

 fensive odor. Similarly, the S may appear as hydrogen 

 sulphide, mercaptans, etc., which are likewise disagreeable. 



It is evident that not only the material which is acted 

 upon, but also the particular species at work will influence 

 the kind of fermentation. Thus, when glucose is acted 

 upon by the yeast, itis changed to alcohol, whereas another 

 organism can convert it into lactic, or into butyric acid. 

 Moreover, it should be understood that a given organism 

 which induces a typical fermentation when grown in a sugar 



