ENZYMS IN MILK 231 



are rarely free from bacteria, and therefore it is difficult to obtain 

 sterile milk in sufficient quantity to make successful experiments. 

 The usual procedure, when studying milk enzyms, is to add an 

 antiseptic, such as chloroform, toluol, etc., which restrains bac- 

 terial activity, but does not materially retard enzym action. It 

 is true that in this manner bacterial activity can be prevented and 

 the production of enzyms inhibited, but enzyms that have been 

 produced previous to the addition of the antiseptic are not ex- 

 cluded. 



Milk enzyms may originate in the circulation and pass through 

 the mammary glands uninjured; they may originate in the mam- 

 mary gland or they may be liberated from disintegrating leu- 

 kocytes. Finally, they may be the result of bacterial metabolism 

 before the milk is drawn from the udder. It must be confessed 

 that our knowledge of the origin of milk enzyms has not reached 

 the point where it can be positively stated that certain enzyms 

 originate from one source or another. There is little doubt that 

 some enzyms which have been found in milk are really of bac- 

 terial origin, but the existence of inherent milk enzyms still awaits 

 positive proof. 



It has been assumed that some enzyms in milk are an aid in 

 digestion, and special stress has been laid upon this point in 

 reference to the use of cow's milk for infant feeding. It is doubt- 

 ful, however, whether enzyms in cow's milk are of real importance 

 to the human infant, for it is natural to assume that, if inherent 

 digestive enzyms actually exist in cow's milk, they would be of 

 little value for another species of mammal. 



A variety of enzyms obtained from milk have been reported 

 in the literature. These include proteolytic, carbohydrate-split- 

 ting, oxidizing, and reducing enzyms. 



Proteolytic Enzyms. Duclaux found a proteolytic enzym as- 

 sociated with rennet and which he considered of importance in 

 cheese ripening. This "casease" can be obtained by precipitating 

 with alcohol a broth culture of Tyrothrix tenuis, a bacterium of 

 the hay bacillus group. Duclaux's casease is a trypsin-like fer- 

 ment. 



A great deal of attention has been given to a ferment discovered 

 in milk by Babcock and Russell and named galactase. This en- 

 zym was found in milk of the cow, sheep, goat, pig, horse, half- 

 breed buffalo, and in human milk. Cow's milk in which the 

 enzym was studied was drawn under aseptic precautions and 

 preserved with an antiseptic. The antiseptics used were chloro- 

 form, ether, benzol, and toluol, but preference was 'given to 

 chloroform as being the most effective. These antiseptics pre- 

 vent bacterial growth, but do not inhibit enzym activity. 



