EXPERIMENT STATION BULLETINS. 203 



butyric acid. Besides Pasteur, Conn, Fitz, Prazmowsky, Hueppe and 

 others have added much to the study of butyric acid fermentation. 



Attention has already been called to its presence in milk, butter and 

 cheese, but its presence elsewhere in nature must not be overlooked. In 

 the intestinal tract there is a certain amount of butyric acid produced by 

 the action of bacteria and in some cases in such large amounts as to 

 render the functions of the lining membrane abnormal and thus produce 

 one form of dyspepsia. Again it is found in some of our food fermenta- 

 tions, as sauerkraut. 



This fermentation may result from the transformation of grape-sugar, 

 starch, lactic acid and albuminous substances. In milk, it is generally 

 considered to be the change of lactic acid and by others to sometimes 

 occur directly from milk sugar. As by-products, carbon dioxide and 

 free hydrogen are eliminated. Inasmuch as this fermentation takes place 

 in the presence of the nitrogenous constituents of the milk, such as 

 casein, there are other products manufactured by a secondary fermen- 

 tation of these micro-organisms which tend to neutralize any acidity 

 present and dissolve or throw in solution the casein. This secondary 

 fermentation may belong to the butyric acid micro-organisms or may 

 be the result of the activity of other micro-organisms. However this 

 may be, ammonia and ammonia compounds and derivatives of ammonia 

 are frequently found present. 



PEPTONIZING FERMENTATION. 



I— 



Intimately associated with the rennet ferment is the peptonizing 

 property of some bacteria. These bacteria are usually those that have the 

 power to produce the precipitation of casein, but the peptonizing action 

 follows that of the rennet action; yet this is not always true, for there 

 are those bacteria which are able to peptonize without the production 

 of any rennet ferment, although they are comparatively few in number. 

 It would seem that these bacteria acted somewhat differently in the pep- 

 tonization of casein, because there are those cases where we have the 

 solution so perfect or the casein so completely peptonized that the milk 

 has become as clear as water; there are those, also, which are able to 

 peptonize the casein only in part, so that the casein remaining settles to 

 the bottom, usually in a gelatinous mass with a watery layer above; and 

 again there are those which peptonize the casein only in part and leave it 

 in a semi-clear condition. 



The .change of the casein is similar to the change of meat in the 

 process of digestion. Our meat is changed into a soluble form before it 

 is assimilated by the organs of assimilation. In the case of casein by the 

 action of this peptonizing ferment, a soluble product is obtained which 

 is closely allied to the soluble product obtained from meat by the process 

 of digestion. This product from meat is known as peptone and from 

 casein as caseon. 



RENNET FERMENTATION. 



Imagine a series of vessels of equal size all having the same amount of 

 milk in them, before you, and in each a single species which possesses the 

 rennet action. You would be able to discern that there is a great variety 



