SO-CALLED ' BIOLOGICAL PROPERTIES ' OF MILK 95 



in milk, it is necessary to collect samples free from bacteria. This 

 was carried out in the first place by Rullmann (1911) and later 

 by Harden and Lane-Claypon. The results obtained by these 

 observers leave little doubt that even when there are no bacteria 

 present, as shown by growth on culture media, or when bacteria 

 are present in such small numbers as to be negligible, traces 

 of catalase are present in most samples. 



Rullmann (4) used twenty samples of milk, and gives the follow- 

 ing figures for the oxygen evolved : 



After i hour 

 After 12-18 hours 

 After 18-24 hours 



Nil, or only a trace. 

 0-2-3-8 c.c. 

 0-3-3-6 c.c. 



Milk which was not entirely free from bacteria showed the presence 

 of rather more catalase when investigated over longer periods, 

 than in the case of the sterile samples. 



The results obtained by Harden and Lane-Claypon showed 

 considerable variation in even the sterile samples of milk. Using 

 50 c.c. of milk, they obtained amounts varying from 3-7 to 6-0 c.c. 

 of oxygen when the time was less than four hours in several cases 

 less than one hour. 



There can be little doubt that there are two sources of origin 

 for the catalase in cows' milk, but the greater part of the catalase 

 in ordinary market milk is of bacterial origin. 



Efforts have been made to connect the catalase with one of 

 the constituents of milk, and the investigations of several observers 

 show that the cream is richer in catalase than other parts of the 

 milk. The catalase, however, has been found to be easily removed 

 from the cream by washing, so that it seems unlikely that the 

 catalase is an integral property of the fat globules. 1 The figures 

 given by Jensen upon this matter are interesting and show also 

 the absence of relationship between the bacteria present in small 

 numbers and the amount of catalase. 



1 Cp. Reiss, Heygendorff and Meurer, Meyer. 



