SO-CALLED 'BIOLOGICAL PROPERTIES' OF MILK 115 



of these investigations was to show that milk which was infected 

 by the cholera organism might safely be drunk, because the bacteri- 

 cidal power of milk would be sufficient to destroy the organism. 

 The investigations as a whole appear to show that the organism 

 died only as soon as the milk became sour. 



A great number of organisms grow very readily in milk, although 

 there is some evidence to show that certain organisms survive at 

 the expense of other strains which die out fairly rapidly in the 

 milk. 1 



Conn and Stocking showed that during the first few hours 

 after milking there was an apparent decrease in the total number 

 of bacteria which was most rapid during the first three hours. This 

 decrease in total numbers was accompanied by a rapid increase 

 in the number of acid-forming bacteria, which not only increased 

 absolutely, but also in proportion to the total organisms present. 

 The following table gives some idea of the results obtained by these 

 workers : 



Many observers have failed to obtain evidence of any bactericidal 

 power of milk. 2 Klimmer, Sommerfeld, and Kolle used cultures of 

 B. Coli or B. Typhosus for their investigations. Cozzolino found 

 some evidence of inhibition of bacterial growth both with human 

 and cows' milk. 



Koning investigated the numbers of bacteria present in the 

 same sample of milk both directly after milking, and at later stages. 

 He obtained evidence of an initial decrease in the number of bacteria, 

 which was most marked in milk collected as far as possible free 

 from bacterial contamination, being less marked in dirty milk. 

 He found the optimum temperature to be 37 C. The decrease 

 in the number of bacteria was not shown in milk which had been 

 previously boiled, and persisted in raw milk for a longer period if 

 the milk was kept cool. He believed that milk contained sub- 

 stances inhibitory to the growth of bacteria, which were probably 

 derived from the blood. 



1 Cp. Conn and Ester. 



* Cp. Schottelius, Moro (3), Klimmer, Sommerfeld, Kolle. 



I 2 



