Kinds of Milh Fermentations. 71 



be found in the milk the bacteria of any germ dis- 

 ease with which the animal may be afflicted, or which 

 may be carried into the milk through the atmosphere, 

 the water used in cleansing utensils, or the persons 

 of individuals suffering from the disease. 



The fermentations of milk. — The normal fermenta- 

 tions to which milk is subject may be conveniently 

 divided into three classes. First, those which feed 

 upon and cause changes in the milk-sugar, known as 

 lactic fermentations. Second, those that feed upon 

 and cause changes in the albuminoids of the milk ; 

 these in turn are of two classes, peptogenic and pu- 

 trefactive. Third, those which attack the fats, and 

 are known as butyric fermentations. Besides these, 

 which may be called normal fermentations, in that 

 they will easily occur in any sample of milk if left to 

 itself, there are a large number of other fermentations 

 which may be called abnormal, from the fact that 

 they occur only in isolated localities, or from time 

 to time. These abnormal fermentations include one 

 which causes the casein of milk to coagulate without 

 the development of lactic acid, known as sweet curd- 

 ling ; another which causes a peculiarly ropy or slimy 

 condition of certain constituents of milk ; still an- 

 other that results in the formation of an intensely 

 bitter product in the milk ; an alcoholic fermenta- 

 tion, and several fermentations which result in the 

 production of various colors, collectively known as 

 chromogenic fermentations. An illustration of this 

 class is seen in the well-known "bloody bread," 

 which is caused by the growth of Bacillus prodigiosus. 



