46 . THE MILK QUESTION 



that term either as it is popularly or scientifically under- 

 stood, for it possesses none of the fundamental properties 

 of life. On the contrary, milk, like other dead organic sub- 

 stances, begins to deteriorate and decompose from the 

 moment it is drawn, and sometimes even before it leaves 

 the udder. 



Milk is sometimes believed to contain life because it is 

 rich in ferments or enzymes. These substances are exceed- 

 ingly active. The chief enzymes found in milk are the 

 catalases, peroxidases, and reductases. One of the princi- 

 pal ferments in milk is galactase discovered by Babcock and 

 Russell. This ferment is capable of slowly dissolving pro- 

 tein substances. Ordinarily the galactase found in milk 

 acts too slowly to cause any material change in the milk 

 proteins in the short intervals which elapse between the 

 withdrawal of the milk from the animal and its consump- 

 tion as food. This ferment may assist digestion when milk 

 is used in a mixed diet. 



The peroxidases are interesting ferments in milk. They 

 are substances capable of inducing the oxidation of guaia- 

 cum and other readily oxidizable substances by means of 

 hydrogen peroxide. The reductases also interest us be- 

 cause they have the power of reducing certain chemicals. 

 Thus they will change the color of methylene blue, an 

 anilin dye. 



The catalases, peroxidases, and reductases are used in 

 the laboratory to determine whether a milk is fresh or old, 

 and whether it has been heated or not. For example, a 

 temperature of 70° C. for half an hour will kill almost all 

 the ferments in milk. If a milk, therefore, does not give 

 the reactions characteristic of the ferments, it is quite 

 certain that it has been heated to a temperature above 

 this point. In an old milk undergoing fermentation 

 the activity of both the reductases and peroxidases is 

 increased. 



The thermal death-point of milk enzymes. The effect of 



