68 MILK AND ITS HYGIENIC RELATIONS 



filtration. It is present in much smaller amounts in the milk than 

 in the blood. 



Experiments on Cows' Milk. One or two of the earlier observers 

 have stated that cows' milk contained a fat-splitting ferment. 

 This has not been confirmed by later observers. Davidsohn, 

 when using cows' milk, was unable to obtain the above-mentioned 

 reaction for human milk. 



Ferments acting on Sugar. Some observations have been 

 carried out with a view to ascertaining whether milk contained 

 a ferment capable of acting on the sugar in milk, i.e. lactose. The 

 investigations are accompanied by considerable experimental 

 difficulties in determining a change of a small order in the quantity 

 of sugar present. The older observers, who worked with milk 

 containing bacteria, believed that they obtained evidence of some 

 action upon the sugar. So many bacteria are capable of fermenting 

 milk-sugar that unless the milk is absolutely germ-free, the dis- 

 appearance of a small quantity of this sugar cannot be regarded 

 as necessarily due to an action in the milk as such. Lactose, 

 when acted upon by the ferment lactase, is split up into two mole- 

 cules of different sugars, namely, one molecule of galactose and 

 one of glucose. This action is known to take place very readily 

 in the alimentary canal of the infant. It has been shown by Aders 

 Plimmer that lactase is present in the alimentary canal of young 

 animals at birth, and in some species of animals even before birth, 

 in considerable amounts, and will rapidly convert the lactose into 

 the simpler sugars, which are then absorbed for the use of the 

 organism. 



Lactase, if present at all in milk, is present only in infinitesimal 

 quantities, and it is more likely that it is entirely absent, and that 

 such disappearance of lactose as has been observed, has been due 

 to bacterial action. Since the sugar becomes converted to the 

 simpler sugars within a very short period of its being taken by the 

 infant, no physiological value can be attributed to the possibility of 

 minute traces of lactase in the milk. 



Briefly, it may be said that cows' milk does not contain ferments 

 capable of aiding the digestion of the substances in milk itself, to 

 an appreciable extent. One of the ferments is present in larger 

 amounts in human milk than in cows' milk, but even here the effect 

 upon digestion in the infant must be regarded as negligible. The 



Eresence of these ferments is almost certainly to be accounted for 

 y filtration from the blood, or as a result of the breaking down 

 of the cells of the gland itself. 



On the Presence of Oxidising Ferments. Reference has already 

 been made to a ferment whose presence has been used to detect 

 previous heating of the milk. This ferment is known as peroxi- 

 dase, because it acts on substances known as peroxides. The 

 literature upon this ferment is extensive. 



The first observations upon the presence of this ferment appear 



