SO-CALLED BIOLOGICAL PROPERTIES ' OF MILK 67 



be regarded as of any value. Investigations carried out by myself, 

 in which experiments were conducted with bacterial-free milk over 

 a period of twenty-four hours, gave no indications of proteolytic 

 action in milk. 



Grimmer, who has carried out much work upon many aspects 

 of milk, has more recently investigated the ferments present in 

 the mammary gland itself. He examined the resting and active 

 glands of a number of animals, and found that a small amount of 

 proteolytic activity occurred when the gland, carefully prepared 

 for experiment, was allowed to stand and to undergo auto-digestion. 

 The action was more marked in the active gland, but in no case 

 was the action strong enough to affect any foreign protein intro- 

 ducedthat is, it was only able to act upon the protein of the 

 gland itself. There seems some possibility of another ferment 

 being present in the active gland which has the power of breaking 

 down simpler substances (polypeptides) derived from proteins. 

 Grimmer states that the presence of these ferments in the gland 

 itself is doubtless due to the necessity for the production of milk 

 protein from the proteins of the gland itself. 



As concerning the proteolytic action in milk itself, after reviewing 

 the literature, he comes to the conclusion that the proteolytic 

 action of milk, if present at all (upon which, he says, the evidence 

 is not very conclusive), is so small that it cannot be regarded as 

 being worthy of any serious consideration as an aid to digestion 

 in the infant. 



Fat-splitting or Lipolytic Ferments. Experimentation upon 

 the presence of a lipase in milk is not easy, and the number of 

 investigations carried out have not been large. 



Experiments on Human Milk. It appears fairly certain 

 that human milk does contain a ferment capable of splitting fatty 

 substances. This action, however, is said to be insufficient to show 

 any action upon fat contained in the milk itself, and is only 

 demonstrable when fatty substances are added to the milk. As 

 a whole, two substances have been used for this purpose, mono- 

 and tri-butyrin, and some evidence has been obtained of the splitting 

 of this substance by human milk. The most important investiga- 

 tions have been those of Davidsohn, who has made some interesting 

 observations. Davidsohn added a few drops of tributyrin to fresh 

 human milk, and found that, after gently shaking for a few minutes, 

 a peculiar smell, that of butyric acid, was produced. He showed 

 that the action of this ferment was connected with the phenomenon 

 of surface tension in the milk, the surface tension being reduced 

 by the action of the ferment. This action is not observed in milk 

 unless tributyrin be added to the milk. He found the ferment 

 both in the whole milk and in the whey, and showed that its action 

 was of a similar type to the fat-splitting ferment present in the 

 blood. There seems no reason to doubt that this ferment is derived 

 from the blood stream, and passes into the milk by a process of 



F 2 



