128 Transactions of the Canadian Institute. (Vol. VII. 



was exactly the same, 0.32 per cent.; but in the former case, the 

 increase was accomplished in six days, and in the latter thirty-five days. 



Whilst the increase in numbers of the lactic acid bacteria can fully 

 account for the initial increase in acid, no ready explanation can be 

 given for the gradual and progressive development of acidity from the 

 sixth to the fortieth day. The acidity is due more to acid salts than to 

 free acid, and it may be that some change occurs in the acid bases, and 

 perhaps some of the fatty acids are liberated. 



The "Period of Rapid Decline" is practically synchronous with the 

 gradual increase of acidity, and the "period of gradual decline" is 

 coincident with the maximum amount of acidity. This increase, 

 followed by an almost permanent amount of acidity, may possibly 

 explain why the bacteria die out at first rather rapidly and subsequently 

 somewhat more slowly, the least resistant germs being killed off quickly 

 by the slow accumulation of acid followed by the gradual death of the 

 stronger individuals. 



Lactic acid bacteria.— T\\& prevalent lactic acid species present in all 

 samples was undoubtedly the B. acidi lactici of Esten. This author 

 stated that this bacterium is identical in every particular with Gunther 

 and Thierfelder's organism. In most of the samples of cheese it was 

 the predominating lactic acid bacterium present. Next in numbers 

 was B. lactis aerogenes, or a form closely allied to it. This microbe 

 curdled milk into a soft curd, and after some time gas bubbles appeared. 

 When cultures of the above two organisms were seeded together in 

 sterilized milk, a firm curd was produced with little or no gas. 

 Occasionally a micrococcus producing a buff-coloured colony, and also 

 torulae were found. Both of these turned litmus red and coagulated it 

 into a solid curd with no separation of whey. 



Gas producing bacteria. — The gas producing bacteria belonged 

 usually to either the B. coli group or else to the B. lactis aeroge?ies 

 group. In the former group many varieties have been cultivated, 

 showing considerable differences as to motility, indol and gas produc- 

 tion. Nearly all writers on dairy bacteriology blame varieties of this 

 bacillus for producing gassy milk and bad flavours. In several 

 instances the cheese was mottled when this germ was present and this 

 result might be possibly brought about by the bleaching action of the 

 hydrogen liberated in the cheese by this ubiquitous microbe. 



According to Weinzirl the "huffing" of cheese results from the 

 activity of a large number of Hueppe's B. acidi lactici. Cohn considers 



