14 BULLETIN 342, U. S. DEPARTMENT OF AGRICULTURE. 



seem to prove this point, it has never been thoroughly established. It 

 has been found that the rate of bacterial increase is approximately 

 the same when the comparison is made between raw milk and pas- 

 teurized milk having about the same bacterial content. 



It is often stated that pasteurization, even if it does destroy bac- 

 teria, does not destroy poisonous products of their growth. This 

 can hardly be considered a real objection, for if they are present in 

 raw milk they must be consumed with it, and if pasteurization does 

 not destroy them the pasteurized milk would be no worse than the 

 raw milk. 



The question as to whether pasteurization destroys beneficial enzyms 

 is still an open one. In the light of our present knowledge of the 

 enzyms in milk and the part they play in the digestive process it is 

 quite impossible to settle the question of their importance. It is 

 evident, however, that the low temperatures now in use in pasteuriza- 

 tion have little effect on the commonly recognized enzyms. 



The opponents of pasteurization have raised an objection on the 

 ground of its direct influence on the milk producer. It has been 

 asserted that pasteurization would cause lax methods of production 

 on the farm, for the reason that farmers would know that the milk 

 was to be pasteurized and, therefore, they could be careless in its 

 production. There seems to be some basis for this objection, but in 

 any city where there is any inspection of the raw-milk supply the 

 same inspection can and should be continued even though the milk 

 is to be pasteurized. 



From a chemical standpoint serious objections have been raised 

 against pasteurized milk, because the heating produces changes which 

 render the milk less digestible, particularly in the case of infants. 

 As has already been stated, however, Rupp has found that milk 

 pasteurized at 145° F. for 30 minutes does not undergo any appre- 

 ciable chemical change. He found that soluble phosphates do not 

 become insoluble, that the albumin does not coagulate, and that when 

 higher temperatures are used chemical changes do occur. He also 

 developed the fact that 5 per cent of the albumin is rendered in- 

 soluble in milk heated for 30 minutes at 150° F., while at 160° F. 

 30.78 per cent of the albumin is coagulated. It is evident that the 

 use of low temperatures for pasteurization overcomes any objections 

 which may be raised on the ground of chemical changes. 



Further evidences that low-temperature pasteurization does not 

 injure the digestibility and nutritive value of the milk is shown by 

 the results of feeding experiments on babies. According to Weld (13) 

 a number of babies that were fed raw milk and pasteurized milk 

 showed only a slight difference in the average net daily gain in 

 weight during the feeding period. The slight difference was in favor 

 of pasteurized milk. 



