[HARRISON] PRESIDENTIAL ADDRESS S 



lactic fermentation but would curdle, putrefy, etc. In fact, he ascer- 

 tained, what subsequent experiments have confirmed, that the lactic 

 acid organism was common in the dairy, but more rare elsewhere. 



To return to the work of Robert Hall, already mentioned and 

 which in point of time comes between Lister's two papers, Hall 

 obtained milk direct from the udder by inserting a sterilized tube into 

 the milk duct and thrusting it upward into the milk cistern, then 

 allowing the milk to flow into sterilized vessels, which were immediately 

 closed to avoid air contamination. By this means, he obtained milk 

 that was sterile and which kept sweet and unchanged. 



This experiment proved that the lactic ferment was not derived 

 from the cow, but was caused by micro-organism gaining access from 

 some external source. This important observation was confirmed by 

 Lister and later by Meisfier and in more modern times by de Feuden- 

 reich and others. 



Bert in 1878 announced that a pressure of several atmospheres 

 would prevent the souring of milk, although such pressure had no 

 effect upon unorganized ferments. Hagemann (1882) noted that 

 bacteria were the producers of lactic acid in milk and the addition 

 of chloroform stopped the action, whilst this chemical was without 

 effect on chemical enzymes. 



Boutroux in 1878 shewed that the growth of the lactic organism 

 was checked by the presence of considerable quantities of acid and 

 that the growth of the organism ceased as soon as there was an accu- 

 mulation of acid. 



Richet in 1879 determined the relation of the organism to various 

 temperatures — finding that the growth of the organism increased 

 up to 40°C and then diminished, ceasing entirely at 52°C. 



In the meantime F. Cohn had demonstrated the presence of 

 spores of bacteria in milk and thus furnished the reason for the diffi- 

 culty of sterilization. 



With the methods of research invented and perfected by R. 

 Koch, especially the use of gelatine and agar and the obtaining of 

 pure cultures by the plate method Dairy Bacteriology received a 

 great impetus, and the pioneer work here outlined was subjected to 

 rapid revision by a host of investigators and was followed by the 

 establishment of new principles in modern dairying practice. 



