76 MILK AND ITS HYGIENIC RELATIONS 



Proteolytic Ferments. In Cows' Milk. A fair number of investi- 

 gations have been carried out with a view to ascertaining whether 

 proteolytic enzymes were present in milk. Prolonged investiga- 

 tions were carried out by Babcock, Vivian and Russell (i, 2, 3, 4) 

 (1898 and 1899), by Freudenreich (1900), and by Boekout and De 

 Vries (i, 2) (1899-1901), all of which were more directly connected 

 with the ripening of cheese than with proteolytic enzymes in milk 

 as such. Babcock and his collaborators collected the milk carefully, 

 but no initial bacterial count was made, and the milk was at once 

 treated with an antiseptic. The experiments were carried out 

 over prolonged periods (weeks or months), the amount of soluble 

 nitrogen present at the beginning and end of the experiment being 

 used as a basis for determining the presence of proteolytic enzymes. 



Freudenreich (1900), who sterilised the milk with ether, obtained 

 no increase in the soluble nitrogen within one month, although a 

 slight increase occurred if the experiment was carried over more 

 prolonged periods. 



Boekout and De Vries (i, 2) found that cheese made from pasteur- 

 ised milk did not ripen, and that the increase of soluble nitrogen 

 which occurs is very small compared with that which occurs with 

 cheese made from raw milk. Bacteria appear to have been present 

 in both forms of milk, and they conclude that the proteolytic 

 activity observed was due to the action of bacteria. 



Babcock and Russell (i, 2) obtained evidence of the formation 

 of albumoses and peptone, but they point out that the products 

 of proteolytic activity, which were ammonia, amides, and peptones 

 are suggestive rather of bacterial than of enzyme action. 



Moro (3) (1902) carried out investigations of the action of milk 

 upon fibrin suspended in this fluid. He obtained evidence of 

 traces of proteolytic activity, but the milk was not known to be 

 free from bacteria. 



Zaitschek (1904) was unable to demonstrate any degree of 

 proteolytic activity other than such as might be within the limits 

 of experimental error. The small amount of activity found by 

 Moro is probably due to the same fact. 



A. J. J. Vandevelde (i), working both alone and with De Waele 

 and Sugg, used milk which was not sterile, but to which acetone- 

 iodoform solution was added. The experiments were carried out 

 over fairly long periods, in no case less than five days, and some 

 evidence of proteolytic activity was found. The degree of action 

 was, however, very variable. 



In none of these observations was initially sterile milk used, 

 and there is no evidence to show that the proteolytic activity was 

 not due to bacteria present in the milk. The addition of antiseptics 

 does not preclude this possibility, since, although the bacteria them- 

 selves may be killed by the antiseptic, yet between the time of 

 milking and the time of their death they may conceivably have pro- 

 duced proteolytic enzymes, which are not destroyed by antiseptics. 



