316 LOUIS PASTEUR 



" M. Pasteur declares that he hopes to be able to realize 

 this result, that is to say, to discover the conditions under 

 which certain inferior plants may live apart from air in 

 the presence of sugar, causing that substance to ferment 

 as the yeast of beer would do." 



This summary and the preconceived views that it set 

 forth have lost nothing of their exactness; on the con- 

 trary, time has strengthened them. The surmises of the 

 last two paragraphs have received valuable confirmation 

 from recent observations made by Messrs. Lechartier and 

 Bellamy, as well as by ourselves, 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 

 1 5th, 1875, we sowed a trace of yeast in 150 cc. (rather more 

 than 5 fluid ounces) of yeast-water, containing 2^/2 per cent, 

 of milk-sugar. The solution was prepared in one of our 

 double-necked flasks, with the necessary precautions to 

 secure the absence of germs, and the yeast sown was it- 

 self perfectly pure. Three months afterwards, November 

 1 5th, 1875, we examined the liquid for alcohol; it contained 

 only the smallest trace; as for the yeast (which had sen- 

 sibly 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 fer- 

 mentation, like a fungoid growth, absorbing oxygen, and 

 evolving carbonic acid, and there is no doubt that the ces- 

 sation 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 entirely 

 of carbonic acid and nitrogen, the vitality of the yeast was 

 dependent on, and in proportion to, the quantity of air which 

 entered the flask in consequence of variations of tempera- 

 ture. 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 





