SO-CALLED ' BIOLOGICAL PROPERTIES ' OF MILK 93 



he found that if fresh milk was inoculated with stale milk H 2 S 

 appeared on the addition of sulphur. He considered that B. coli 

 was especially active in the production of H 2 S from sulphur. 



Rullmann (4) , using milk which was obtained sterile by means of 

 the milking-tube, was unable to detect hydrogenase in any case. 

 He concluded that the formation of sulphuretted hydrogen from 

 sulphur was bacterial in origin. 



Catalase. The ferment to which this name is given has the 

 property of splitting hydrogen peroxide with the evolution of 

 molecular oxygen, after the equation 



2H 2 O a = 2H a O + O 2 . 



The early investigators did not differentiate catalase from the 

 other ferment-actions noticed by them, but observations of Bach 

 and Chodat, confirmed by Neumann-Wender (i), showed definitely 

 that catalytic activity was separate from the other ferment actions. 



The use of hydrogen peroxide for the preservation of milk 

 was suggested by Budde*, and the process so introduced is known 

 as buddisation. This process was investigated by Chick, who 

 worked upon the presence of catalase in milk in order to test the 

 value of hydrogen peroxide as a preservative. Chick showed 

 that milk had the power of splitting hydrogen peroxide, but that 

 the addition of fairly large amounts of this reagent removed this 

 power. Concurrently with the disappearance of the reaction, 

 the milk became sterile owing to the bacteria being destroyed. 

 She showed further that when milk, which had been rendered 

 approximately sterile by boiling, received the addition of a small 

 amount of raw milk, the capacity for splitting hydrogen peroxide 

 gradually returned. These facts pointed to the production of 

 catalase by bacteria present in the milk, but did not preclude 

 the presence of catalase in the milk apart from that produced by 

 bacteria. 



Method of Estimation of Catalase. The amount of catalase 

 present in milk is estimated by ascertaining the amount of hydrogen 

 peroxide which is split by the enzyme, as measured by the amount 

 of oxygen evolved. It is necessary to shake the apparatus used 

 at frequent intervals, or a correct estimation of the oxygen is not 

 obtained. Evidently also precautions must be taken to equalise 

 the pressure inside and outside the apparatus. 



Various authors have designed different methods for the estima- 

 tion of catalase. For the most part 10, 15, or 20 c.c. of milk have 

 been employed, to which 3 or 5 c.c. of a weak solution of hydrogen 

 peroxide have been added. Many observers use a 3 per cent, 

 solution of the peroxide ; others have used a weaker solution. 



The apparatus is usually kept in a water-bath, and the experi- 

 ment does not extend over a prolonged period. Descriptions of 

 the methods used will be found in the papers by Koning, Burn 



