18 PASTEUR: THE HISTORY OF A MIXD 



Experiment, questioned in this fashion, gave an imme- 

 diate response. All the paratartrates examined appeared 

 with their two epaulets, that is to say with all the faces 

 required by the laws of symmetry: there was no more 

 hemihedrism: the facet on the right had its corresponding 

 one on the left and, simultaneously, every trace of action 

 on polarized light had disappeared. 



This was a confirmation of Pasteur's foresight, a re- 

 ward of his daring intuition. But, in addition to this 

 foreseen discovery, chance, one of those happy chances 

 which one rarely meets with save when he is constantly 

 in search of it, kept in store an unexpected discovery. 

 Among the paratartrates there were two which behaved 

 differently when they were crystallized. The others gave 

 crystals having hemihedral facets in pairs, and conse- 

 quently had no hemihedrism, just as he is no longer one- 

 armed who has two arms. On the contrary, the double 

 paratartrates of soda and ammonia on the one hand, of 

 soda and potash on the other, deposit in their mother 

 liquors crystals which are all hemihedroms, all one-armed; 

 only there are some of them which have the right arm, 

 and others the left. 



What did this mean? If one regarded these facts as 

 a whole, the result was confusing, since it showed the 

 apparition of hemihedrism where there was no rotary 

 power. But Pasteur had advanced too far to go back. 

 He had already derived too much advantage from his 

 conception to lose confidence. ''In spite of all that was 

 unexpected in this result," said he,^ ''I followed none 

 the less my idea. I separated with care the right and left- 

 handed hemihedral crystals and observed separately 

 their solutions in the polarization apparatus. Then, 

 with no less surprise than joy, I saw that the right- 



* Recherches sur la dissjTn<?trie moleculaire. Le^on professee a la 

 Soci6t6 chimique de Paris, 1860, p. 29. 



