SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 89 



showed reducing power for methylene blue. He considers that 

 if reduction occurs in 



Less than 3 hours the milk is of poor quality. 

 In 3-7 hours the milk is of fair quality. 

 In over 7 hours the milk is of good quality. 



Reduction in less than one hour, i.e. a quarter or half an hour, 

 denotes a bacterial content of fifteen to twenty millions ; if the period 

 is over seven hours the content will be less than one million per c.c. 



Bertin-Sans and Gan joux (2) were unable to establish any relation- 

 ship between the reduction time and the bacterial content. Their 

 results, however, agree generally with those of Fred, as they consider 

 that milk which reduces M.B. in a quarter of an hour must be 

 regarded as bad, and pasteurised milk should not effect reduction in 

 less than seven hours. 



Schardinger's Reaction. The importance of a reliable test 

 for boiled milk in contradistinction to raw milk has already been 

 pointed out, and it has been shown that the peroxidase reaction 

 has been largely used for this purpose. Evidently, when the 

 boiled milk can have the property upon which the test rests restored 

 by some artificial means after it has been boiled, the value of the 

 test is almost at once negatived. 



Utz pointed out that the results obtained with Schardinger's 

 reagent depended upon the alkalinity of the milk. Milk, when 

 fresh, has an alkaline reaction, but stale milk having an acid re- 

 action did not give the F.M.B. test. Utz (2, 3), however, showed 

 that the reduction could be restored even in sour milk by the addition 

 of an alkali. If this is the case, evidently Schardinger's test 

 cannot be regarded as a reliable one for the previous boiling of 

 milk. 



The matter was further considered by Siegfeld (2), who believed 

 it to be unreliable, and by Rullmann (2, 5), who believed that the 

 reaction was positive even after the milk had been heated to 68 C. 1 



Several later observers have dealt with the restoration of the 

 Schardinger reaction by the addition of alkali and also by the 

 addition of an iron solution to milk which has been boiled. Brand 

 showed that the addition of alkali, even to raw milk, aids the 

 F.M.B. reaction, which cannot be reproduced in boiled milk by 

 this means. Koning confirmed these results, but showed further 

 that the addition of lactose to sterilised or boiled milk is capable 

 of restoring the F.M.B. reaction. 



Romer and Sames showed that even when milk has ceased to 

 give Schardinger's reaction it will at once do so if a small amount 

 of i per cent, solution of ferrous sulphate be added. The reaction, 

 however, is negative if the ferrous sulphate has been previously 



1 Cp. also Utz (5), Schardinger (2). 



