MILK AS A FOOD 47 



heat upon the activity of the ferments in milk is very sim- 

 ilar to the effect of heat upon ferments or enzymes from 

 other sources. Indeed, they are all very much alike and all 

 of this great group of substances stand in such intimate and 

 close relation to the vital activity of the cell that all those 

 conditions which destroy the one, tend also to destroy the 

 other. 



In general, the ferments have a higher thermal death- 

 point than the bacteria. The activity of most of the fer- 

 ments begins to diminish at 60° C. and is seriously af- 

 fected at 70° C, and at 80° C. they are destroyed. The 

 non-sporebearing bacteria are destroyed at 60° C. It is 

 therefore possible to destroy all the serious infections in 

 milk so far as man is concerned without influencing its 

 "life" so far as the ferments are concerned. In fact, it 

 has been shown that milk heated to 60° C. increases the 

 activity of some of the ferments, notably the peroxidases. 

 All of the bacteria in milk cannot be destroyed without ren- 

 dering the ferments inactive. This is because some of the 

 bacterial spores must be heated to the boiling-point or 

 over in order to kill them. It is fortunate that the harm- 

 ful, non-sporebearing bacteria perish when exposed to 

 heat before the ferments are seriously affected. It is for- 

 tunate because the ferments are the nearest approach to 

 life we know of in milk and they probably exercise a 

 favorable influence in digestion and nutrition. 



The thermal death-point of the other vital principles in 

 milk, such as antitoxins, opsonins, agglutinins, and other 

 antibodies, are all approximately 60° C; that is, they are 

 destroyed at about the same temperature necessaiy to 

 kill non-sporebearing bacteria. 



Colostrum 



The secretion of milk during the first few days after the 

 birth of all mammalian animals varies markedly in composi- 

 tion and in amount from the milk secreted during any other 



