192 MILK HYGIENE 



distinctly marked upon the bottle or can, and the milk 

 must not be permitted to go upon the market until the 

 method has received official sanction. Sterilized milk 

 should be sold only with a statement of the way in which 

 sterilization has been done, and not until after the 

 method has been inspected and approved. But it is not 

 enough merely to establish such requirements ; the sani- 

 tary officers must see to their enforcement, partly by vis- 

 iting the pasteurizing and sterilizing establishments, 

 partly by taking samples and examining the milk sold. 

 Fortunately, it is possible to determine by chemical 

 means whether milk has been heated to 80° C. (176° F.) 

 or not. These tests are based on an observation by 

 Arnold and have been develo^Dcd by Babcock, Storch and 

 others.-'^ ^ The principles are the following: 



Starch's method: 5 e.e. of milk are poured into a test tube; a 

 drojD of weak solution of hydrogen dioxide (about 0.2 per cent.), 

 which contains about 0.1 per cent, sulphuric acid, is added, and 2 

 drops of a 2 per cent, solution of paraphenylendiamin, then the 

 fluid is shalcen. If the milk or the cream becomes, at once, indigo 

 blue, or the whey violet or reddish brown, then this has not been 

 heated or, at all events, it has not been heated higher than 78° C. 

 (172.5° r.) ; if the milk becomes a light bluish gray immediately or 

 in the course of half a minute, then it has been heated to 79° to 80^ 

 C. (174.2° to 176° F.). If the color remains white, the milk has been 

 heated at least to 80° C. (176° F.). In the examination of sour milk 

 or sour buttennilk, lime water must be added, as the color reaction is 

 not shown in acid solution. 



Arnold's guaiac method: a little milk is poured into a test tube 

 and a little tincture of guaiac is added, drop by drop. If the milk 

 has not been heated to 80° C. (176° F.), a blue zone is formed 

 between the two fluids; heated milk gives no reaction, but remains 



'-''^ Heating milk to a high temperature coagulates the albumin 

 and globulin and the milk loses its property of curdling by the 

 action of rennet. By this change one may discover that it has 

 been heated, but not determine whether the milk has been heated 

 to 80° C. (176°F.), that is, if it has been pasteurized. 



