226 MILK AND ITS HYGIENIC RELATIONS 



of desiccation, milk is exposed on rollers which are heated to a 

 temperature of approximately 120 C. This exposure, however, is 

 for a very short period only, and it has been shown by Delepine 1 

 that the maximum temperature probably does not at any time 

 exceed 96 C., and that the duration of the exposure to that 

 temperature approximates to 3-3 seconds. It need not therefore 

 be anticipated that any appreciable change takes place in the 

 protein of milk on desiccation. The albumin is probably in part 

 coagulated, but there is no loss, since the whole of the dried milk 

 is utilised. The work given in Chap. XII bears out the above 

 remarks. 



Slight changes in viscosity occur in the fat when heat is employed, 

 but no diminution in content appears to be noted below a tempera- 

 ture of 100 C. or even somewhat above this temperature. The 

 cream line is said to be affected at 150 F. approximately, but this 

 is probably related to the changes in viscosity already alluded to. 



No change occurs in the lactose content unless the temperature 

 be raised considerably above 100 C., when a brownish colour may 

 occur which indicates that some caramelisation has taken place. 



The so-called ' biological properties ' have been studied with 

 a view to determining the effect upon them of heat. Ferments 

 are destroyed by a temperature of 100 C., or below, but as there 

 is no reason to suppose that these, when present in milk, are of 

 any value, the question of their destruction does not call for 

 consideration. 



The properties which are concerned in immunity have also 

 been the subject of investigation, but it cannot be said as yet that 

 the results are entirely harmonious. It seems probable that 

 where any alteration has been observed as a result of the heating 

 of milk, this can be referred to the coagulation of the albumin or 

 perhaps to the reduction in the calcium content of the fluid. In 

 a number of cases where the effect of heat upon the reactions for 

 immunity has been studied, no change has been detected when 

 the temperature has reached 100 C. or even higher. It has been 

 shown in Chap. VI that these properties are only of value to the 

 suckling animal in the early days of life. In any case, therefore, 

 the effect of heat after this period needs to be considered only in 

 relation to the nutritive properties possessed by the proteins to 

 which the properties are attached. This has already been done in 

 the preceding chapters, where the satisfactory results obtained by 

 the use of boiled milk have been dealt with in detail. 



There is no evidence to show that the reduction in calcium 

 content which occurs when milk is boiled, has any influence on 

 the human infant when artificially fed. Such other acid or basic 

 radicals which may be present in the milk and appear to be slightly 

 reduced by heating, are present in considerable excess in cows' 



1 Cp. Appendix F. 



