.INTRODUCTION. xiii 



pursuing the line that he has chosen, and in which 

 his labours have rendered him one of the most con- 

 spicuous scientific figures of this age. 



With regard to the earliest labours of M. Pasteur, 

 a few remarks supplementary to those of tyL Eadot 

 may be introduced here. The days when angels 

 whispered into the hearkening human ear, secrets 

 which had no root in man's previous knowledge or 

 experience, are gone for ever. The only revelation 

 and surely it deserves the name now open to the wise 

 arises from ' intending the mind ' on acquired know- 

 ledge. When, therefore, M. Eadot, following M. Pas- i/ 

 teur, speaks with such emphasis about ' preconceived 

 ideas/ he does not mean ideas without antecedents. 

 Preconceived ideas, if out of deference to M. Pasteur 

 the term be admitted, are the vintage of garnered 

 facts. We in England should rather call them induc- 

 tions, which, as M. Pasteur truly says, inspire the 

 mind, and shape its course, in the subsequent work 

 of deduction and verification. 



At the time when M. Pasteur undertook his inves- 

 tigation of the diseases of silkworms, which led to 

 such admirable results, he had never seen a silkworm ; ^ 

 but, so far from this being considered a disqualification, 

 M. Dumas regarded his freedom from preconceived 

 ideas a positive advantage. His first care was to 

 make himself acquainted with what others had done. 

 To their observations he added his own, and then, 



