GERMS IN RELATION TO MILK 23 



The kind of germs which will grow in milk depends on the 

 temperature of the milk. Below 6o° F. miscellaneous perms grow, 

 but those which sour milk do not flourish. Therefore in dirty 

 milk which kept for some days below 50 F. the miscellaneous 

 germs may be abundant. These, or the poisons they produce, may 

 cause disease in the human being — chiefly nausea and vomiting, and 

 cholera infantum. The harmless lactic acid germs flourish at room 

 temperature (6o° — 70 F.). Comprising less than 1% often in 

 new milk, in 24 hours at room temperature they may reach 50%, 

 and in 48 hours 95% of all the germs in the milk. At this time 

 the milk sours, the acid having killed all the other germs. 



At temperatures between 8o° and ioo° F. various different 

 kinds of germs may predominate, but often the germs which lead 

 to formation of gas in milk and cheese are in most abundance (B. 

 lactis aerogenes). 



It will thus be noted that sweet milk may be much more harm- 

 ful to health than sour milk, i. e., if it was contaminated and has 

 been kept sweet by means of a low temperature. 



There is a large class of germs known as putrefactive germs 

 because they produce changes in milk which are akin to rotting of 

 meat. If these continue to develop long enough they may impart 

 a bad odor to milk or its products and are likely to induce diarrhceal 

 diseases in children. 



Among the more common putrefactive bacteria which work 

 harm to milk are the " liquefiers." They enter milk in manure and 

 filth and thus to a considerable degree indicate contamination of 

 milk with filth. 



The liquefiers may at first cause " sweet curdling " in milk 

 from the action of a rennet-like ferment they produce. Later — or 

 sometimes immediately — the liquefiers alter and dissolve the casein 

 of milk by means of another ferment (casease) which digests the 

 casein. The milk then becomes clear as water or variously colored 

 and has a putrid odor. 



