238 MILK AND ITS HYGIENIC RELATIONS 



of the body in the same manner as the protein molecules from 

 which they were derived. 



Such experimental work as has been carried out has, for the 

 most part, been concerned with the forensic or legal side of the 

 question. The object has been to determine a method either for 

 differentiation of raw and boiled milk, or for the detection of pro- 

 teins of different species. For this purpose the methods which have 

 been considered in Chap. Ill have been employed, based upon the 

 production of anti-sera by the injection of raw or heated milk. 



There is some lack of uniformity in the results obtained, much of 

 which can probably be explained by the different methods used. 

 In the early investigations no differentiation of the antigens was 

 made, the whole milk being injected. It was shown in Chap. Ill 

 that such a method will produce a complex result since several 

 different antigens are injected, each producing its own effect. 



Further, in the preceding pages it has been shown that heat 

 reduces the amount of soluble albumin. Hence when milk is 

 heated before injection the amount of soluble antigen which will 

 be injected will be reduced, and the degree of reduction will vary 

 with the duration of the period of application of heat before in- 

 jection. 



Caseinogen is not so readily affected by heat, although this 

 occurs when high temperatures are used. 



A number of the investigations upon the effect of heat on the 

 antigens of milk have been concerned with milk which had been 

 boiled for prolonged periods frequently for half an hour or 

 raised to temperatures above the boiling-point of water. In these 

 circumstances there will be a decrease, or even perhaps an absence, 

 of soluble albumin in the fluid injected. 



No experiments appear to have been performed with heated 

 albumin alone, and it is impossible to ascertain from the original 

 papers whether the precipitated albumin was used in the injection 

 or not. In view of the differences in the methods of heating, it is 

 likely that in some cases the albumin remained in the vessel, and 

 in others where the milk was only just boiled that the albumin 

 was present in the injected fluid. 



Some observers who have used the precipitin reaction, have 

 concluded that the divergent results were attributable to the 

 variation in the calcium content occasioned by heating the milk. 



The results obtained by different observers are shown in the 

 table on p. 239. 



Bauer (1910) found that caseinogen as an antigen was not 

 affected by being boiled, and regarded the effect of heat upon the 

 antigens in milk as attributable to the effect on the albumin. This 

 view is confirmed by the work of Rudicke and Sachs, who found 

 that a lacto-serum produced by injecting milk which had been 

 boiled for half an hour, did not react with the homologous serum 

 although it did react with the homologous milk. It will be 



