8O THE TYPES OF MILK BACTERIA. 



belong to the lactic type, the milk may still be looked upon 

 as not fresh, but not badly contaminated (see Chap. IX.). 

 If the number, however, is large and the majority of them 

 belong to this liquefying type, the indications are that the 

 milk has been subjected to some excessive source of filth 

 contamination and is more suspicious. 



This type of bacteria has very little to do with the changes 

 which ordinarily occur in milk. It is true that they are able 

 to produce profound changes in the chemical nature of the 

 milk, even more profound than those of the first type, but 

 their development is commonly prevented by the lactic bac- 

 teria, and in ordinary milk they get no opportunity to grow. 

 It is rare that any changes occur in the ordinary milk supply 

 which are to be attributed to this type of organisms, although 

 it occasionally happens. Once in a while a dairyman finds 

 what is called sweet curdling, due to some of these organ- 

 isms. Occasionally also putrefactive tastes may develop 

 in the milk, and these again are due in all probability to this 

 type of microorganisms. But in the majority of cases the 

 rapid development of lactic bacteria checks the growth of 

 this type of organisms, so that they do not produce any 

 noticeable effect upon the milk. That they probably have 

 some influence in the changes that occur in -ripening cream 

 we shall see in a later chapter. 



MISCELLANEOUS. 



The lactic- and enzyme-forming bacteria may be regarded 

 as normal to milk, inasmuch as they are expected in 

 nearly every sample of milk. In addition to these, there 

 is a large variety of occasional visitants which may produce 

 more or less change in the character of the milk. Inasmuch, 

 however, as they are found only occasionally they are prop- 

 erly to be regarded as infections of the dairy. When abund- 

 ant they may produce trouble for the dairyman which is 

 sometimes very serious. In their relation to dairying they 



