294 THE MILK QUESTION 



is gradually dying out, for the requirement is a necessary 

 and reasonable one. 



Heat, instead of cold, has been proposed to preserve 

 milk. If kept hot enough, milk may be preserved in- 

 definitely. If milk is kept at a temperature above that at 

 whiqji bacteria grow, say about 120° F., it may be pre- 

 served even more satisfactorily than by the use of ice. 

 Very few bacteria grow at this temperature and practically 

 none of those ordinarily found in milk. Milk may thus be 

 kept for a long period of time. The plan, however, is not 

 practical; in fact, it is almost impossible to carry out, and 

 is exceedingly hazardous for the reason that if the temper- 

 ature is not very carefully maintained, the milk will drop 

 to about 100° F., at which temperature bacterial multipli- 

 cation occurs at its best. 



Milk is sometimes heated to the temperature of pasteur- 

 ization and higher for a short period of time as a preserv- 

 ative. Pasteurization, however, should never be used as a 

 preservative. 



Adjusting milk 



It is now generally recognized that the mixing of milk 

 from various cows is desirable. Mixed milk furnishes a 

 more uniform product, as it eliminates individual varia- 

 tions in composition and it also has a tendency to dilute 

 infections which may be present. There is no special ob- 

 jection to marketing milk from mixed herds, but there is 

 another form of mixing or adjusting which needs the serious 

 consideration of the health ofiBcer. Some dairymen add 

 just enough cream to skim milk to make it comply with 

 the legal percentage, sell this as normal milk, and make 

 money. In fact, to prevent illegal blending or adjusting 

 milk according to scientific manipulations now requires the 

 watchfulness of the law, for such manipulations have to a 

 large extent taken the place of the old-style crude watering 

 or skimming. When milk is diluted with skim milk instead 

 of water, it is rather diflScult to detect. 



