78 PASTEUR: THE HISTORY OF A MIND 



such as sugared water, the new globules live at the ex- 

 pense of substances which the older globules have 

 allowed to diffuse into the liquid. All are famished and 

 then the young consume the old. It is this work of 

 diffusion and of exhaustion of globules already formed 

 in order to feed the young, which caused the diminishing 

 weight of the yeasts sown by Thenard in the sugared 

 water in the experiments cited above, and which has 

 led to the belief that the yeast is destroyed in fermenting 

 the sugar. In reality, there were not enough of the 

 new globules formed to compensate for the loss of weight 

 which the old globules underwent as the result of the 

 diffusion but if we add to the weight of the globules the 

 weight of the soluble organic matter which the filter does 

 not retain, but which we can find and estimate in the 

 liquid, we see that this total weight always increases 

 during the fermentation, because there is always a little 

 sugar which becomes yeast. 



In proportion as the fermentation is accomplished 

 under better conditions and the yeast is less exhausted 

 toward the end, the increase in weight is more notable. 

 We are aware of this from the fact that the yeast con- 

 tinues to give off carbonic acid at the expense of its own 

 tissues for some time after all the sugar has disappeared 

 from the liquid which bathes it. We would say to-day 

 that it consumes the reserve food which it has made, 

 for it is a provident little cell which stores up in a time 

 of plenty for a time of famine. How is it possible not to 

 see that all this is a question not of decomposition and 

 of death, but, on the contrary, of development and 

 of life? 



