34 LOUIS PASTEUE. 



the former differed from the latter by the complete . 

 absence in its case of molecular dissymmetry. 



With regard to other facts of the same kind, an- 

 nounced not only in France, but in Italy, and in 

 England chiefly the pretended formation of grape 

 tartaric acid from succinic acid, artificial and inert, 

 by Perkin and Duppa Pasteur testified with absolute 

 certainty of judgment to the existence of phenomenal 

 peculiarities proper to these substances, which he had 

 never seen, and which had, on the other hand, been 

 the object of careful study by observers of great talent. 



After these verifications and deductions from 

 theoretic views, Pasteur discovered a surprising con- 

 nection between the prior researches of chemistry and 

 crystallographic physics and the new and entirely un- 

 expected results of physiological chemistry. This 

 connection, like the thread of Ariadne, conducted him 

 to his recent great discoveries in medical biology. 

 M. Chevreul was right when, some years ago, at the 

 Academy of Sciences, he expressed himself thus : 



' It is by first examining in their chronological order 

 the researches of M. Pasteur, and then considering 

 them as a whole, that we are enabled to appreciate 

 the rigour of judgment of that learned man in form- 

 ing his conclusions, and the perspicacity of a mind 

 which, strong in the truths which it has already dis- 

 covered, is carried forward to the establishment of new 

 ones.' 



