Preservation of Milk. 107 



general milk supplies that may be used by children is lit- 

 tle short of criminal. The sale of these preparations for 

 use in milk finds its only outlet with those dairymen who 

 are anxious to escape the exactions that must be met by 

 all who attempt to handle milk in the best possible man- 

 ner. Farrington has suggested a simple means for the 

 detection of preservalin (boracic acid). 1 When this sub- 

 stance is added to fresh milk, it increases the acidity of 

 milk without affecting its taste. As normal milk tastes 

 sour when it contains about 0.3 per cent lactic acid, a milk 

 that tests as much or more than this without tasting sour 

 has been probably treated with this antiseptic agent. 



Physical methods of preservation. Methods based upon 

 the application of physical forces are less likely to injure 

 the nutritive value of milk, and are consequently more 

 effective, if of any value whatever. A number of methods 

 have* been tried more or less thoroughly in an experimental 

 way that have not yet been reduced to a practical basis, as 

 electricity, use of a vacuum, and increased pressure. 2 Con- 

 densation has long been used with great success, but in this 

 process the nature of the milk is materially changed. The 

 keeping quality in condensed milk often depends upon the 

 action of another principle, viz., the inhibition of bacterial 

 growth by reason of the concentration of the medium. 

 This condition is reached either by adding sugar and so in- 

 creasing the soluble solids, or by driving off the water by 

 evaporation, preferably in a vacuum pan. Temperature 

 changes are, however, of the most value in preserving milk, 

 for by a variation in temperature all bacterial growth can 

 be brought to a standstill, and under proper conditions 

 thoroughly destroyed. 



1 Farrington, Journ. Amer. Chem. Soc., Sept., 1896. 

 Hite, Bull. 58, West Va. Expt. Stat, 1899. 



