VI PREFACE. 



dissymmetry, down to his most recent investigations 

 on hydrophobia, on virulent diseases, and on the arti- 

 ficial cultures of living contagia, which have been 

 converted by such cultures into veritable vaccines 

 passing by the intermediate celebrated experiments on 

 spontaneous generation, fermentation, the diseases of 

 wine, the manufacture of beer and vinegar, and the 

 diseases of silkworms the author of these pages has 

 been able, if not to witness all, at least to follow in 

 its principal developments this uninterrupted series of 

 scientific conquests. 



' What a beautiful book,' he remarked one day to 

 M. Pasteur, ' might be written about all this ! ' 



'But it is all in the Comptes-rendus of the 

 Academy of Sciences.' 



' It is not for the readers of the Comptes-rendus 

 that such a book needs to be written, but for the great 

 public, who know that you have done great things, 

 but who know it only vaguely, by the records of 

 journals, or by fragments of biography. The persons 

 are few who know the history of your discoveries. 

 "What was your point of departure ? How have you 

 arrived at such and such principles, and at the conse- 

 quences which flow from these principles ? What is 

 the connection and rigorous bond of your method ? 

 These are the things which it would be interesting to 

 put together in a book which would have some chance 

 of enduring as an historic document.' 



