70 MILK AND ITS HYGIENIC RELATIONS 



siderations, influencing the effect of the reaction, have not been 

 taken into due consideration. As a result, there is a great deal of 

 discrepancy between the observations of the numerous investigators 

 who have dealt with this subject. Some assert that heating to 

 75 C, the temperature which was believed by Storch to be sufficient 

 to prevent the reaction occurring, is inadequate. Others state 

 that 70 C. is sufficient if the milk be kept at this temperature for 

 half an hour, and so on. Where the length of time of heating 

 and the temperature to which the milk has been raised are unknown, 

 and the reaction not very marked, difficulty is likely to arise in 

 determining whether the milk can be considered to have been 

 heated or not. 



Further, where the dairyman desires that it should not be 

 known that the milk has been heated, the addition of a small 

 proportion of raw milk causes the reaction to return, and un- 

 less full precautions are taken, and a considerable series of observa- 

 tions carried out, the observer may be entirely deceived as to the 

 presence of a large amount of heated milk. In spite of these draw- 

 backs, however, no other method appears to be available for 

 determining whether milk has been heated or not. 



Much controversy has arisen in regard to the chemical mechanism 

 which produces this reaction in milk. For some years past a discus- 

 sion has been proceeding between several German dairy chemists as 

 to the true state of affairs in regard to this substance. It is stated 

 on the one hand that the reaction is not due to a ferment at all, 

 and that it depends for its production upon the reaction of the 

 milk, which must be alkaline for the production of this reaction ; 

 also that, even having due regard to the alkalinity, the presence 

 of iron is instrumental in bringing it about. The opposite state- 

 ment is that this reaction is a true ferment action inasmuch as, 

 although it does depend upon the alkalinity of the milk, it is only 

 in part dependent upon the reaction, and depends also upon the 

 physical condition of the protein present in the milk. If the 

 protein is in any way altered, the reaction is not produced, although 

 the milk may be of the necessary alkalinity. 



A number of observers have dealt with the relationship of this 

 reaction to the presence of iron. It seems probable that it is con- 

 nected with the presence of iron in colloidal form, and possibly also 

 of manganese. This presents no difficulty when considered in 

 relation to milk, since it has already been shown that iron is 

 constantly present in milk, and the investigations which have been 

 made show that the amount of iron present in cows' milk, although 

 small, is quite sufficient to produce this reaction. Infinitesimally 

 small quantities of manganese have also been found in the ash of 

 milk by several observers. The full mechanism of this reaction 

 is even now not entirely understood, but for the present purpose 

 no difficulty is presented. 



On the Presence of Peroxidase in Human Milk. Numerous 



