244 



this exception has not been firmly established ; some germs are 

 said to assist in the process of digestiiig the milk in the alimen- 

 tary canal. This supposition, however, is in want of positive 

 proof. Experiment station men say that sour milk, which 

 contains less nutrient material than sweet milk, will generally 

 produce better results when fed to pigs than similar milk in a 

 sweet condition. WoU says that this may be due to the stimu- 

 lation of the appetite by the lactic acid in the sour milk, or in 

 its aiding digestion by increasing the acidity of the stomach 

 juices. 



Sour Milk.— The class or group of bacteria that act on 

 milk sugar and produce lactic acid are very numerous and aie 

 nearly always present in the milk. They multiply so rapidly 

 that the milk soon becomes very sour. As a rule these lac- 

 tic acid-producing bacteria grow more rapidly than any other 

 germs, especially until the quantity of acid reaches 8 per cent.; 

 then the lactic acid germs cease to grow. The germ that is 

 said to be the most common lactic reagent is Hueppe's Bacillus 

 iickli lactici. This germ will not grow in milk when the lac- 

 tic acid reaches the limit of .8 per cent.; yet all the milk sugar 

 is not changed into lactic acid. Several kinds of acid produc- 

 ing bacteria may be growing at the same time in the milk ; 

 but, as a rule, one kind soon gains the ascendancy. 



In the process of "ripening cream" one or more of the lac- 

 tic acid-producing bacteria are used. Sometimes most of the 

 accidental germs are destroyed by heating the cream or milk 

 to about 158 degrees F.; after cooling it to below 100 degrees 

 iF., the cream or milk is inoculated with a specific germ that 

 will produce the ripening or souring, and at the same time 

 .give a pleasant taste and aroma to the butter. As a rule, if 

 the milk and cream are kept clean the ripening will take 

 place as the result of the few germs that accidentally infect 

 them ; and the butter will have a pleasant taste and aroma. 



The lactic acid-producing bacteria form the greatest num- 

 ber of accidental germs in milk ; they are non-spore forming 

 bacteria and consequently can be killed by heating the milk 

 to 158 degrees F. for 20 or 30 minutes. 



Alkaline-Producing Germs. — There are several bacteria 



