BACTERIA IN MILK 21 



different species of bacteria that have the power of pro- 

 ducing lactic acid. Milk containing only lactic acid bac- 

 teria is spoken pi as a "pure culture" or "starter." Such 

 cultures are now a commercial product and should be 

 used wherever fancy butter and cheese and sour milk 

 products are desired. The method of using these pure 

 cultures or starters is discussed in the chapter on cottage 

 cheese making, page 90. 



Bacteria that Produce Taints and Bad Odors. 

 While the lactic are the commonest bacteria of milk, 

 there are always present many other types, some of which 

 produce serious taints and bad odors. Bacteria of this 

 kind are usually associated with filth, and dairies that be- 

 come strongly infected with them show lack of cleanliness 

 in the care and handling of the milk. 



The commonest bad flavors produced by this class of 

 bacteria may be designated as rancid, bitter, strong, gassy, 

 oily, fishy, and putrefactive. In market milk these filth 

 bacteria are objectionable not only because of the bad 

 flavors they produce, but also because they are recognized 

 as a common cause of infantile troubles, such as diarrhoea. 

 The high mortality among bottle-fed babies has been 

 shown to be largely due to drinking milk that has been 

 produced under unsanitary conditions. 



Disease Producing Bacteria. Milk frequently be- 

 comes infected with this class of bacteria through diseased 

 cows, infected water, infected milk vessels, and diseased 

 attendants. 



One of the commonest of the disease producing bacterw 

 is the bacillus tuberculosis. This germ usually finds 

 entrance into the milk in two ways : It may come from 

 the cow directly through her milk, or it may gain access 

 to the milk through the litter in the barn. No milk should 



