Fermentations of Milk. 89 



garicus type, which apparently enter the milk with the 

 fecal matter. The nature of the change produced by 

 them in milk is very similar to that caused by Bact. 

 lactis acidi in that lactic acid is the chief product; no 

 gas is produced and hence the curd is uniform in ap- 

 pearance. Temperatures from 100 to 110 F. favor 

 their development. Organisms belonging to this group 

 are used in the preparation of the fermented milks now 

 so widely sold in the cities. 



These desirable, acid-forming bacteria are of the 

 greatest service in every branch of the dairy industry, 

 whether in butter or in cheese making, or in the sale 

 of milk in the city. The dairy industry is dependent 

 upon fermentative activity, as much as the manufacture 

 of beer or wine, and the main basis of this is the acid 

 fermentation of the milk by these desirable types of 

 bacteria. 



Although milk contains a large amount of nitro- 

 genous substances (casein and albumen), it does not 

 undergo putrid decomposition, as do meat and eggs, 

 not because it is not fitted for the growth of the bac- 

 teria causing that type of change, but because the acid 

 formed in it stops the growth of the putrefactive bac- 

 teria. If a sample of milk is placed in a stoppered bot- 

 tle, it will have much the same taste and odor at the 

 end of several months as at the end of a few days. The 

 acid acts as a preservative, like the vinegar in pickles, 

 or the acid in silage and in sauerkraut. Meat placed 

 in a stoppered bottle which is then filled with milk will 

 be preserved. 



The products formed in the decomposition of meat 

 and eggs are not only offensive but may also be injuri- 



