376 EXPERIMENTS WITH PLANTS 



sign of souring ? It appears that the souring of milk is 

 diie to bacteria. 



Our stab cultures have shown us that while there 

 are comparatively few bacteria in perfectly fresh rnilk, 

 they increase very rapidly, so that after standing a few 

 hours the milk is full of them. Some of these bacteria 

 cause the souring of milk, others impart disagreeable 

 flavors and odors (if the milk is allowed to stand long 

 enough) ; some seem to have no effect on the milk, 

 while still others produce the agreeable flavor of butter 

 and cheese. These latter may be procured in pure cul- 

 tures by dairymen, and added to their butter or cheese 

 to produce the desired flavor. 



In milk may occur bacteria which produce typhoid, 

 diphtheria, scarlet fever, cholera, tuberculosis (dis- 

 puted), and intestinal troubles (cholera infantum). 

 The infection may come from the cow, from the people 

 who handle the milk, or from water. In Stamford, 

 Connecticut, there occurred in 1895, 386 cases of 

 typhoid, of which 97 per cent were on the route of one 

 milkman who rinsed his cans in cold water from a 

 polluted well. Milk- cans and utensils should be care- 

 fully sterilized, and scrupulous cleanliness both of the 

 animals and the persons who handle the milk is highly 

 desirable. 



In order to keep milk from souring, it may be 

 boiled, by which process the bacteria are mostly killed; 

 but since many persons find the flavor of boiled milk 



