196 BACTERIA IN AIR, SOIL, WATER, AND MILK 



to remain at a temperature permitting the growth of 

 bacteria. If kept below 60 F. and used within twenty- 

 four hours the consumer is probably safe at all times. 



Spoiling of Milk. In the summer conditions for the 

 spoiling of milk are more favorable than in winter, 

 since the temperature is unfavorable for its preser- 

 vation, and more dust and flies introduce bacteria. 

 Bottles in which milk is served should be washed 

 when empty, with cold water first, and then boiled or 

 well scalded. If a small quantity of milk remain in 

 the bottom putrefactive and fermentative bacteria grow, 

 and dry on the bottle making it harder to clean 

 subsequently. Milk bottles should be considered as 

 possible carriers of disease and the user should assume 

 his part of the responsibility by cleaning them out 

 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 fulgaricum 

 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 koumys. 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. 



