66 MILK AND ITS HYGIENIC RELATIONS 



the amount given off by a known quantity of milk can be estimated. 

 The reaction has not proved extremely reliable, since this ferment 

 is also readily formed by a number of the bacteria which may 

 have gained access to the milk after its collection, and also to 

 the fact (which will be considered in detail later) that diseased 

 conditions of the udder do not universally produce a rise in the 

 content of this ferment in milk. The literature, therefore, is con- 

 cerned with the ferments in milk in connection with several different 

 matters. In this work the main consideration must be directed 

 to the presence of ferments from the point of view of the nutrition 

 of the infant or young animal, although it will be impossible to 

 omit some consideration of the other aspects. 



On the Possible Value to Infants of the Ferments present in Milk. 

 There are two ways in which ferments in milk might be useful to 

 the infant. They might either assist in the digestion of the food 

 material contained in the milk after it has been taken by the infant, 

 or they might conceivably act as subsidiary agents in connection 

 with the digestive processes, although not themselves directly 

 concerned. In view of the specificity of ferments, the first point, 

 namely, the digestion of the substances in milk itself, is evidently 

 concerned only with such ferments as are capable of attacking and 

 altering the various food materials present in the milk. These have 

 been shown in the previous chapter to consist of nitrogenous 

 substances, or proteins, of carbohydrate, or sugar, and of fatty 

 substances. Inorganic constituents do not require consideration, 

 from this point of view. We are, therefore, first concerned with 

 the investigation of the presence of such ferments as can attack 

 the organic substances, and afterwards with those having a possible 

 subsidiary action. 



Proteolytic Ferments, i.e. those acting on Proteins. Various 

 observers have carried out work upon this matter, but in several 

 cases the milk was not free from bacteria at the time of investigation. 

 Proteolytic ferments are produced by a considerable number of 

 bacteria, hence when these latter are present it cannot be assumed 

 that the milk itself contained these ferments. The earliest investi- 

 gations were carried out in connection with the ripening of cheese 

 by Babcock and Russell (1897). The work of these observers 

 is chiefly interesting as being the earliest observations upon this 

 point, but in view of the fact that the milk was not free from bacteria, 

 they do not call for detailed consideration here. Further infor- 

 mation is given in Chap. V. No subsequent observer found any 

 marked proteolytic action in milk, although several observers 

 obtained evidence of the breaking down of a small portion of the 

 protein when the experiments were carried out over a prolonged 

 period. For the present purpose such experiments are of com- 

 paratively little interest, because milk, when taken by the infant, 

 is digested within a few hours after it enters the body, so that 

 experiments conducted over a period exceeding a few hours cannot 



