TYPES OF BACTERIA FOUND IN MILK 



39 



Bact. lactis acidi, but if it has been kept at 80 or above, it is 

 more likely to be soured by the Bact. aerogcncs type. Milk 

 soured at high temperatures there- 

 fore commonly contains left-handed 

 lactic acid, while that soured at low 

 temperature contains right-handed 

 acid. 1 These facts are of special 

 importance in cheese making as will 

 be noted later. 



PEPTONIZING AND RENNET 

 FORMING BACTERIA 



At times the dairyman is puzzled 

 by a somewhat unusual phenomenon, 

 for he finds his milk curdling, but 

 not becoming sour, and he speaks of 

 the phenomenon as "sweet curdling.'! 

 It is apt to occur in the fall or 

 spring, when the food of the cattle 

 is being changed. It is due to a 

 class of bacteria that have the power 

 of secreting certain chemical fer- 

 ments very similar to those produced 

 by the digestive glands of the stom- 

 ach and intestine. 



Upon almost any gelatin plate made 

 from milk (see page 280) there will 

 be found, in addition to the colonies 

 of lactic acid bacteria, a number of pits in which the gelatin is 

 being dissolved or liquefied. This effect is produced by bacteria, 

 and if a platinum needle be dipped into one of these pits and then 



FIG. 21 LIQUEFACTION OF 

 GELATIN BY ENZYME- 

 FORMING BACTERIA 



1 Ferguson. Die spontane Zersetzung der Milch. Gottingen, 1902. 

 .Conn. Ann. Rep. Storrs. Exper. Sta., 1906. 



