GERMS IN RELATION TO MILK 5 



It does not even curd on heating. The proteids of the milk are, 

 Ihowever, transformed into cleavage products owing to digestion of 

 ".the casein by the peptonizing or digestive action of the bacteria. 



Such decomposed milk may be harmful or actually poisonous, 

 and all milk kept sweet over long periods by cold alone is to be re- 

 garded as unfit for food — especially for infants. 



The number of germs developing in milk at the freezing temper- 

 ature is considerably greater than in milk kept at room or body 

 temperatures after the elapse of several weeks. Freezing, therefore, 

 'does not necessarily destroy germs — as, for instance, the germs of 

 typhoid fever have remained alive in ice for a period of three months 

 — but this temperature retards their growth (see p. 6) and many 

 lands of germs are killed by it. Ice water is therefore compara- 

 tively free from germs. The most favorable temperature for the 

 .growth of disease germs is that of the animal body — from 98 F. 

 to 103 F. — while most other germs multiply most readily between 

 the temperatures of 59 F. and yj u F. 



This knowledge is of the greatest importance in the care of 

 milk and teaches us that the chief essential consists in cooling it 

 immediately to a low temperature (40 F. to 50 F.) and keeping 

 it at this temperature thereafter till consumed. The number of 

 ;germs in milk is always estimated as that number contained in a 

 •cubic centimeter of milk. A cubic centimeter represents a cube 

 holding a quantity of liquid equivalent to about one-quarter of a tea- 

 spoonful, or sixteen drops of water. If very clean milk is kept below 

 50 F. for 24 hours there is not only not an increase but generally a 

 decrease in the number of germs, and the same usually holds good 

 for very clean milk kept 36 hours below 45 ° F. The initial decrease 

 in the number of germs in new milk is due to a feeble and variable 

 ^germ-destroying substance present in fresh milk. Immediate cool- 

 ing does not affect the germicidal substance, but heating milk may 

 destroy it (see p. 10) . The bactericidal body in milk does not lower 

 the number of bacteria in milk which is kept at high temperatures — 



