THE ORGANISMS IN YEAST. 215 



fermentative changes ; and, as was remarked by Dr. Charlton 

 Bastian in a paper read before the Pathological Society of London, 

 in 1875, "it was not until twenty years afterwards that Pasteur an- 

 nounced, as the result of his apparently conclusive researches, that 

 low organisms acted as the invariable causes of fermentation and 

 putrefaction, and that such changes, though in fact chemical pro- 

 cesses, were only capable of being initiated by the agency of 

 living units." Having shown thus much, M. Pasteur proceeded to 

 demonstrate that, not only were the living cells the active cause of 

 change, but that the nature of the change varied according to the 

 species of cell-life employed ; that any one species of such cell- 

 life was not capable of conversion into any other variety ; and that 

 one species would flourish in a medium in which another could not 

 continue to live. It should be borne in mind that these investiga- 

 tions were carried on in connection with the industrial processes of 

 brewing and wine-making, and that therefore the results obtained 

 have especial bearing upon the present subject. 



It was necessary at the commencement to obtain supplies of 

 the various moulds and ferments free from admixture one with the 

 other, and from extraneous cell-life, which might interfere seriously 

 with the experiments, and for this purpose a plan was adopted 

 which serves at the same time to prove the universal presence of 

 these agents of change in the atmosphere and elsewhere. Liquids 

 capable of sustaining the growth of such ferments as it was desired 

 to study were placed in glass flasks, the necks of which were 

 drawn out to a point before the blow-pipe, and after certain means 

 had been taken to destroy whatever vital germs they might con- 

 tain, they were hermetically sealed and put by for long periods, in 

 order to see v/hether their contents remained unchanged. When 

 a number of such flasks had remained a considerable time without 

 exhibiting any sign, either of fermentation or of life, they were 

 taken to various parts of the building wherein the laboratory was 

 situate — some, even, into the garden — when, the narrow extremity 

 of the neck being broken, air was admitted. The flasks were 

 then immediately re-sealed, and were restored to their former 

 position upon the shelves of the laboratory. In a few days the 

 presence of small specks of mould upon the surface of the liquid 

 within, or the rising of big bubbles of gas, gave evidence that with 



