SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 73 



Several methods have been used for the estimation of the gas 

 (oxygen) evolved as a result of the action of this ferment upon 

 hydrogen peroxide, when added to milk. Some of the methods 

 are fairly reliable, others appear to be less so. It is necessary 

 for the apparatus to be shaken constantly or at very frequent, 

 intervals, if an approximately accurate estimate of the total gas 

 evolved is to be obtained. Some of the methods do not provide 

 for this. 



The amount of oxygen collected from milk collected free from 

 bacteria is very small, although somewhat variable. It has been 

 shown by various authors * that the catalase rises with the cream, 

 and that if separate estimations be made of the oxygen evolved 

 from the first milk, middle milk, and strippings, the content gradually 

 rises as the end of milking is reached. 



Rullmann, and Harden and Lane-Claypon, working on sterile 

 milk, found that small quantities of oxygen were evolved even 

 when there was no evidence of any bacteria present in the milk. 

 Rullmann 's results showed that in the first hour practically no 

 gas at all was evolved, but that after eighteen to twenty-four hours 

 the amount obtained from 20 c.c. of milk varied between o - 2 and 

 3'6 c.c. Harden and Lane-Claypon obtained larger quantities in a 

 few cases, but much variation in the amount evolved was shown. 



This brief summary of the large amount of work which has 

 been carried out, which is described more fully in Chap. V, 

 shows that catalase is present in milk which is uncontaminated by 

 bacteria, in variable but always in small amounts. It is not known 

 whether catalase plays any part at all in nutritional processes. It has 

 been suggested by several authors that the almost universal presence 

 of catalase in tissues has for its object the immediate splitting up 

 of any peroxide which might be formed, which substances are 

 believed to be detrimental to the life of the cells. It is difficult 

 to attribute any importance to the small quantities of catalase 

 present in fresh milk, especially when compared with the large 

 amounts present in the blood. It is almost certain that the catalase 

 present in the milk from a healthy gland, is derived from the blood 

 by the process of filtration. Additional proof of this is afforded 

 by the fact that in diseased conditions of the udder or in the later 

 stages of lactation, when the milk assumes more of the characteristics 

 of serum, the catalase content tends to be increased. 



On Catalase in Human Milk. Numerous investigations have 

 been conducted as to the presence of catalase in human milk. 

 There is a general concensus of opinion that catalase is present, 

 but the amounts show great variations, both from day to day in 

 the same woman, and between different women. As a whole, it is 

 probably present in larger amounts when the gland is working 

 feebly, owing to the poor health of the mother, and at the beginning 



1 Cp. Reiss, Jensen, and others. 



