210 BACTERIA IN AIR, SOIL, WATER, AND MILK 



and not leave it entirely to the milkman. The author 

 knows of one instance where a milk bottle was used 

 as a spittoon. 



Souring of Milk. The souring of milk is due to a 

 variety of bacteria, chief among which is Bacterium 

 lactis aerogenes, related to the Bacterium bulgaricum 

 described above. This germ is ubiquitous. It is not 

 pathogenic. It produces a fermentation of the sugar 

 of milk, lactose, into lactic acid. Moulds may help this 

 and oftentimes lactic acid and ethyl alcohol may be 

 formed side by side. The latter predominates in the 

 carbonated milks like koumyss. Other bacteria cause 

 clot, or precipitation of the casein, the forerunner of 

 cheese. Streptococci from the udder or manure may 

 also help in souring. 



To make buttermilk in the home is a simple matter. 

 A quantity of whole or skim milk is boiled and cooled. 

 A tablet containing the lactic acid bacilli, a small 

 quantity of pure culture of the organism, or a "starter" 

 from a previous making is then added to this cooled 

 milk and set aside in a warm room (about 75 F.) over- 

 night. The result is a rather agreeable sour milk. 

 Pharmaceutical chemists and laboratories are now r 

 supplying tablets and cultures for this purpose. (See 

 page 188.) 



Diseases Caused by Polluted Milk. Many diseases are 

 believed to be due to bad or polluted milk. If milk 

 merely carry the germs this is easily understood, but 

 as is the case in the diarrheas of infants, the trouble 

 may lie not w r ith the bacteria introduced with the 

 milk, but with the disturbance of digestion caused 

 by the abnormal chemical conditions brought about 



