222 PASTEUR: THE HISTORY OF A MIND 



ton, on the branches of vines in the open, these clusters 

 which up to this time could not enter into fermentation 

 after the crushing of their berries, would ferment under 

 the influence of the germs which they could not fail to 

 receive in then* new position. This was precisely the 

 result which I obtained." 



It is clear that in the presence of these results, nothing 

 was left of the mediocre experiments of Bernard. It 

 was certain that the germs of the yeast were brought 

 periodically to the vine by an external plant, on the nature 

 of which Pasteur could make only some plausible hy- 

 potheses, and furthermore, on which we are not yet exactly 

 informed. If I have dwelt so long on this last demon- 

 stration of Pasteur, it is not simply to consolidate an 

 already established proof, but to show, by an example 

 which seems to me typical, how Pasteur was able to 

 broaden the problems which he approached. 



The problem which he had placed before himself in 

 the preceding experiments was apparently very limited: 

 it was the origin of yeasts. Behold how he enlarged it: 



"May I be permitted," he continued immediately 

 after having written the lines which precede, "to enter 

 here into an experimental digression, very worthy of 

 interest? I have said that the clusters of ripe grapes 

 carry on their surface the germs of ferments which pro- 

 duce the wine in the vat and in the casks of the vine 

 grower. Consequently, is it not probable that at the 

 time of the harvest the rains may collect many of these 

 germs and spread them over the soil of the vineyard? 

 Experiment confirms these suppositions. Having de- 

 posited very small quantities of earth from a vineyard 

 in a series of tubes which contain the must of grapes 

 sterilized by a preliminary boiling, I have seen this must 

 undergo alcoholic fermentation in many of the tubes 

 of each series. Without injuring the success of the 



