100 SCIENCE AND PRACTICE OF DAIRYING. 



pure culture of the bacilli in question a sufficient quantity of fresh 

 skim-milk which has been once, or oftener, heated to 70 C., and 

 then cooled to the temperature required for souring, viz., about 

 16 C., then to allow it to become sour, and when this has been 

 accomplished to use it as a souring agent. The cream to be soured 

 may be previously Pasteurized, and, it is hardly necessary to men- 

 tion, should be carefully protected from contamination. The daily 

 employment of pure cultures of lactic ferment for cream souring 

 can scarcely be expected to come soon into regular practice, and no 

 wide-spread demand appears to exist for them as yet. On the 

 other hand, in course of time such pure cultures will probably 

 come to be used more and more, and the more so as it becomes 

 better understood that undesirable properties in butter have pro- 

 bably their origin in the improper souring of the cream. 



42. Different Kinds of so-called Milk Diseases (Milch -fehler). 

 Occasionally it happens that milk or cream coagulates without any 

 previous lactic fermentation. For example, we need only cite the 

 coagulation of boiled milk, in which the reaction is neutral, and 

 the cheesy appearance assumed by cream, in which the precipitation 

 of caseous matter is certainly not effected by lactic acid. The co- 

 agulation of milk of neutral reaction, spoken of by some as sweet- 

 milk coagulation, is effected by means of different kinds of bacteria, 

 which Duclaux has grouped under the name tyrothrix. These 

 fission fungi, which for the most part belong to the group of the 

 so-called potato bacilli, give rise to enzymes of the nature of rennet, 

 which precipitate the caseous matter in milk possessing a neutral or 

 even a slightly alkaline reaction, and which in time dissolve more 

 or less perfectly the coagulated mass. If milk which has been 

 repeatedly boiled does gradually coagulate, and this while showing 

 an almost entirely neutral reaction, such a condition points to the 

 presence of bacteria of this class, whose lasting spores have been 

 enabled to withstand the boiling temperature which has destroyed 

 the lactic bacilli. 



Many disturbances of milk, which occur in creaming and in the 

 preparation of butter, and the causes of which were formerly sought 

 for in disease of the cows, in the influence of weather, and espe- 

 cially in the physiological action of certain foods, that is, in quite 

 erroneous causes, have now, through bacteriological investigation, 

 been certainly traced to fission fungi. 



Where premature or unusually rapid coagulation occurs, there 



