Preservation of Milk. 103 



the milk is drawn, and subsequently holding the milk at 

 temperatures unfavorable to the multiplication of the rela- 

 tively few organisms that do gain access; or (2) by remov- 

 ing those organisms wholly or in part after they have once 

 gained access to the milk. If all are not eliminated, it 

 then becomes necessary to keep the milk under such con- 

 ditions as to check the growth of those which are not re- 

 moved. 



Preservation by exclusion. The first method is followed 

 in many dairies that supply high-grade milk for city deliv- 

 ery. The so-called " sanitary " or u hygienic " milk is usu- 

 ally a milk that has been handled in such a way as to pre- 

 vent the introduction of most bacteria that under ordinary 

 conditions would find their way into the same. The merits 

 of a milk of this character in comparison with one pre- 

 served by means of other methods, as pasteurization, is 

 a question concerning which there has been much discus- 

 sion. When it is considered, as will be shown later, that, 

 methods of preservation can be successfully applied thafc 

 will not apparently change the chemical and physical prop- 

 erties of milk, it is an open question that must be decided 

 in each case whether exclusion of bacteria can be as eco- 

 nomically and efficiently performed as the destruction of 

 the living organisms by heat. Certain it is that the pro- 

 cess of exclusion must be confined to dairies that are under 

 individual control. The impossibility of exercising ade- 

 quate control with reference to the milking process and the 

 care of the milk immediately thereafter, when the same is 

 produced on different farms, is evident. 



In enhancing the keeping quality of milk by removing 

 the bacteria it is necessary to do so without in any way 

 materially interfering with the nutritive qualities of the 



