SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 71 



observers have investigated the peroxidase reaction in human 

 milk with varying results. In some cases peroxidase has been 

 stated to be present ; in others no trace of it has been detected. 

 It seems reasonable to suppose that when present it is present only 

 in small quantities, and that frequently it is entirely absent in huroaa 

 milk. Some observers (Spolverini, Marfan and Gillet, Friedjung 

 and Hecht) believed that the ferment is more constantly present 

 in colostrum than in the later milk, and that its presence is probably 

 due to the leucocytes, which are more numerous in colostrum than 

 later. But even in colostrum no reaction was obtained in a certain 

 number of cases. Friedjung and Hecht examined 174 samples 

 of milk, and found the reaction to be negative in 114 cases. Some 

 observers have failed to detect any peroxidase in the samples of 

 milk examined by them, and have consequently believed that it 

 was absent in human milk. 



Efforts have been made to trace an effect upon the progress of 

 the infant according as peroxidase was present in the milk of its 

 mother or not. These have been entirely unsuccessful, no difference 

 being detectable in the progress of the infants. 



Summary of the Position in regarc? to Peroxidase in Milk. It 

 appears that peroxidase is constantly present in cows' milk, but 

 that its presence is extremely inconstant in human milk. There 

 is no reason to believe that it has any effect upon nutrition. The 

 fact of its frequent absence in human milk would in any case tend 

 to the belief that its effect was negligible. 



Reductases, or Reducing Ferments. The presence of these 

 substances has caused as much discussion as that connected with 

 the previous ferment, peroxidase. The early investigators dis- 

 covered that the bright blue coloration, produced on the addition 

 of methylene blue in small quantities to milk, frequently disappears 

 if the milk is incubated, the milk becoming quite white. It was 

 noticed that the time required for the colour to disappear varied 

 considerably in different samples of milks. The disappearance of 

 the colour is due to chemical changes which take place in the 

 methylene blue. It is not necessary for the present purpose to 

 enter into a long account of the reduction of methylene blue alone. 

 It is now universally admitted that this reaction is brought about 

 solely by the bacteria which have obtained access to the milk 

 after milking. Efforts have been made to utilise this reaction 

 to standardise the number of bacteria present and to enable an 

 estimate to be arrived at of the ' goodness ' or otherwise, of the milk 

 for purposes of sale. But this is not a satisfactory procedure, since 

 only certain strains of bacteria will effect this reduction, and no 

 indication is given of the number of bacteria present which do not 

 decolorise methylene blue. This reaction is frequently known as 

 the direct reductase reaction. 



In 1902 Schardinger published a paper in which he showed that 

 milk, when quite fresh, did not reduce methylene blue alone, but 



