CHANGES PRODUCED IN MILK BY HEAT 237 



In any case, it is difficult to attribute a high degree of importance 

 to the delay in clotting of cows' milk produced as a result of heating. 

 Many of the investigators have brought forward this fact as an 

 argument to show the denaturisation of the protein as a result of 

 heating, and have straightway deduced from this that some harmful 

 effect was probably produced. If, however, it be the case that 

 human milk does not form into a solid coagulum in the infant's 

 stomach, it seems reasonable to suppose that the soft, flocculent 

 coagulum formed in cows' milk which has been heated, will be more 

 favourable for the digestion of the human infant than the solid 

 clot formed with raw milk. 



The Biological Properties of Milk. Ferments. The work of 

 numerous authors, already detailed in Chap. V, shows the very 

 small importance, if any, of the ferments which are normally 

 present in milk. It is unnecessary, therefore, to deal with any 

 possible loss of nutritive or biological properties which might occur 

 in a milk as a result of the destruction of the enzyme content by 

 heat. Where the initial value is negligible, a reduction in value 

 cannot be regarded as occurring. 



On the Effect of Heat upon the Properties concerned with the 

 Production of Immunity. The work which has been considered 

 in Chap. VI has afforded evidence as to the direct absorption 

 of native protein (with such properties as may be attached to the 

 molecule), in the early days of life. Some absorption of foreign ' 

 protein seems also to occur, but only in small amounts ; more- 

 over, there is some reason to suppose that such absorption may 

 not be beneficial to the suckling animal. There can be no doubt 

 that the natural food is of the greatest importance in the early 

 days of life, and such food would be subjected to heat, only in 

 special circumstances, which have been considered in Chap. IX. 



The clinical results obtained by the use of heated cows' milk 1 

 for infants render a consideration of the effect of heat upon 

 the so-called ' protective substances ' of academic interest only ; 

 especially in view of the fact that such properties are destroyed 

 by digestion. In spite of these practical considerations, there has 

 been some amount of discussion in regard to the so-called 'dena- 

 turisation ' of the milk protein by heat. It has been asserted that 

 if the precise temperature at which such a process occurred could 

 be ascertained, it might be permissible to heat the cows' milk used 

 for artificially-fed children to just below that temperature. Such 

 arguments have little weight, and have presumably been advanced 

 without adequate consideration of the processes of digestion. It 

 is a matter of common physiological knowledge that proteins are 

 broken down to their simpler groupings before absorption. These 

 groupings have no ' biological ' properties, and have been shown 

 to be capable, when given by the mouth, of supplying the needs 



i See Chap, XL 



