STUDIES ON FERMENTATION. 171 



liquid is itself sufficient to exhaust the small quantity of 

 yeast, quickly checking the feeble fermentation which it had 

 induced, so feeble indeed as frequently not to be detected by 

 the eye, from the fact that the amount of liquid present is 

 more than sufficient to dissolve any bubbles of carbonic acid gas 

 that might otherwise have been liberated. 



It is a remarkable fact that the yeast, which during its pro- 

 tracted stay in the sweetened water becomes enfeebled to such a 

 degree that it can no longer excite the least fermentation in 

 that water, but will remain in its presence for an indefinite 

 time in a state of inert dust, does not die. In some of my 

 experiments the yeast has remained alive in the sweetened 

 water for more than two years.* It is almost unnecessary to 

 point out that these results are altogether out of keeping with 

 the various properties that are usuallj^ attributed to j^east.f 



In these experiments we may use yeast-water J instead of 

 water sweetened with sugar. Into some flasks of pure yeast- 

 water we put a little yeast, taking all precautions to prevent the 

 introduction of foreign germs. No fermentation results, there 

 being no sugar present ; the yeast, however, begins to bud, and 

 this budding is more or less marked according to the quantity 



* The alcoliolic ferments in general, subjected to these weakening 

 influences, have not all the same power of resistance. That one which 

 seems to possess this power in the highest degree is the saccharomyces 

 pastorianus, which ferment we had in view in writing the above. 



t The term exhaustion {epuisement), which we have just used, was, 

 perhaps, not altogether felicitously chosen. No doubt wo exhaust the 

 cells of yeast when we sow an imponderable weight of them in a large 

 quantity of sweetened water ; it might, however, be better to say that in 

 such a case we adopt a particular method of preserving the vitality of 

 the cells, without suffering them to die of exhaustion, or to multiply by 

 budding. We may remark that the yeast, in this case, exists in a state 

 of latent life, which resembles that of cells on the surface of fruit. The 

 cells on the surface of fruits, bunches, or barks, can no more find around 

 them sufficient aliment for their propagation than can our yeast-cells in 

 a great excess of sweetened water. We would not, however, say of the 

 spores on the surface of fruits, or their woods, that they are in a state of 

 exhaustion ; the term would be misapplied. 



X See foot note p. 79.— D. C. R. 



