216 PASTEUR: THE HISTORY OF A MIND 



which, in the Jura, is toward the end of July, we can 

 introduce into a fermentable juice bits of the fruit and 

 fragments of the stem of the cluster without any fermen- 

 tation of this juice, provided we work carefully and 

 avoid every chance of the introduction of germs other 

 than those which we wish to study. But, as the grape 

 ripens and the day of the harvest approaches, there is 

 an increase in the number of grapes and fragments of 

 the stem which carry the yeasts with them into the juice 

 in which they are sown. The wood of the cluster is at 

 this time more charged with germs than the fruit, which 

 is, itself, more richly supplied than the wood of the 

 branch or the twigs of the vine. Even at the moment 

 of the harvest, not all the grapes are carriers of germs 

 capable of fermenting them, and one may crush them 

 individually and even by twos in sterile flasks, that is 

 to say, place their superficial pellicle in contact with 

 their juice without seeing the latter ferment. Then, 

 after the harvest, when we have made it by collecting 

 only the grapes, leaving behind the stem of the cluster, 

 the germs of yeast upon the latter gradually become fewer 

 and fewer, so that by December and throughout the 

 winter there are none at all. There remain on it only the 

 germs of molds. 



This first question when solved gave rise to another. 

 In what state, on the surface of the berry and on the wood 

 of the stem, do we find these germs of yeast, the existence 

 of which we have just demonstrated? Washing these 

 surfaces with a clean badger's-hair brush, we obtain a 

 clouded drop which, under the microscope, shows nothing 

 resembling yeast. We see there only numbers of 

 corpuscles (A, B, Fig. 19) of a more or less deep brown 

 color or reddish yellow color, with thick and opaque 

 walls, and other more translucent cells, none of which 

 give the idea or present the aspect of the familiar yeasts. 



