SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 87 



similar substance, or (2) that the reaction was due to the ' living 

 protoplasm ' of the bacteria. He believed the latter to be a more 

 likely explanation. 



This latter view was also that of Cathcart and Hahn, who in 

 the same year had demonstrated the power of many bacteria to 

 reduce methylene blue, and who believed that the property was 

 probably attached to the protoplasm of the cell. 



Schardinger's reaction was most marked at a temperature of 

 45-5o C, the colour usually disappearing within thirty minutes 

 after incubation. 



Schardinger's work showed that it was likely there were two 

 separate actions in milk connected with the reduction of methylene 

 blue. Schardinger himself believed that this reduction could be 

 used as a means for detecting the difference between raw and 

 boiled milk. For a time, work upon the reduction of methylene 

 blue was concentrated upon this latter point, but no decisive result 

 was obtained. Gradually the work turned more particularly upon 

 the cause of the two reactions of methylene blue, and it was shown 

 by numerous observers that Schardinger's reaction was probably 

 due to a ferment, the reduction of methylene blue alone being due 

 to bacteria. 



Another series of observations was concerned with endeavouring 

 to utilise the reduction of methylene blue alone, as a method of 

 estimating the number of bacteria present. The efforts, however, 

 resulted in failure. 



On the Differentiation between Direct and Indirect Reductase. 

 A number of investigators have followed up Schardinger's 

 original paper in regard to the differentiation between the reaction 

 with F.M.B. in fresh milk and the reaction with M.B. alone, in milk 

 which has been kept for some hours. 



Smidt (i) showed that there were three factors in milk 

 which could bring about the reduction of methylene blue (he 

 appears to have regarded this action as a catalytic one). 



These three factors were : 



1. Lactose, or other substances which became alkaline on 



boiling, 



2. Ferments, and 



3. Bacteria. 



Smidt showed that fresh milk a few hours after milking 

 gave a positive reaction with Schardinger's reagent but not with 

 methylene blue alone. The reaction with formalin-methylene 

 blue was weakened by heating to 70 C. and destroyed by heating 

 to 75 C. for twenty minutes. He considered this reaction to be 

 due to a ferment which he called aldehyde-catalase. 



The rate of reduction of methylene blue alone, depended upon 

 the number of bacteria present and was in direct relation to it. 



