STUDIES ON FERMENTATION. 265 



have lost nothing of their exactness ; on the contrary, time has 

 strengthened them. The surmises of the last two paragraphs 

 have received a valuable confirmation from recent observations 

 made by Messrs. Lechartier and Bellamy, as well as by our- 

 selves, an account of which we must put before our readers. 

 It is necessary, however, before touching upon this curious 

 feature in connection with fermentations to insist on the 

 accuracy of a passage in the preceding summary, the statement, 

 namely, that yeast could multiply in an albuminous liquid, 

 in which it found a non- fermentable sugar, milk-sugar for 

 example. The following is an experiment on this point: — 

 On August 15th, 1875, we sowed a trace of yeast in 

 150 c.c. (rather more than 5 fluid ounces) of yeast-water, 

 containing 2^ per cent, of milk-sugar. The solution was 

 prepared in one of our double-necked flasks, with the neces- 

 sary precautions to secure absence of germs, and the yeast 

 sown was itself perfectly pure. Three months afterwards, 

 November 15th, 1875, we examined the liquid for alcohol ; it 

 contained only the smallest trace ; as for the yeast, which had 

 sensibly developed, collected and dried on a filter paper, it 

 weighed 0*050 gramme (0"76 grain). In this case we have 

 the yeast multiplying without giving rise to the least fermenta- 

 tion, like a fungoid growth, absorbing oxygen, and evolving 

 carbonic acid, and there is no doubt that the cessation of its 

 development in this experiment was due to the progressive 

 deprivation of oxygen that occurred. As soon as the gaseous 

 mixture in the flask consisted entirel}'- of carbonic acid and 

 nitrogen, the vitality of the yeast was dependent on, and in pro- 

 portion to, the quantity of air which entered the flask in conse- 

 quence of variations of temperatui'e. The question now arose, 

 was this yeast, which had developed wholly as an ordinary 

 fungus, still capable of manifesting the character of a ferment ? 

 To settle this point we had taken the precaution, on August loth, 

 1875, of preparing another flask, exactly similar to the pre- 

 ceding one in every respect, and which gave results identical 

 with those described. We decanted this on jSTovember 15th, 



