12 PASTEUR: THE HISTORY OF A MIND 



This goes to show, and Biot was well aware of this 

 fact, that the action exerted by the solutions of tartaric 

 acid or of sugar is not due, as in quartz, to the arrange- 

 ment of the molecules in relation to each other, that is to 

 the form of construction, but to the shape of the molecule 

 itself, a form which must be related to its constitution. 



It is a considerable stride which this conception forced 

 us to take. It enabled us to attack a question which 

 Haiiy had neglected and which Delafosse had scarcely 

 touched the question of the form of the molecule. It 

 enabled us to see in the arrangement of the atoms of this 

 molecule dissymmetrical dispositions, analogous to that 

 of the integral molecules of the quartz crystal in the 

 arrangement of the crystal. As to the quartz itself, it 

 had awakened ideas, but its importance diminished much 

 in comparison with substances which had the rotary 

 power within the molecule. With the watches in his 

 show-case a watchmaker can make regular geometrical 

 arrangements analogous to some of the crystalline 

 systems; these attract the eye and are subject to certain 

 laws, but as soon as we see that all these watches are 

 going and indicating the same hour we cease to think 

 of the arrangement in the show-case and reflect rather 

 on the movement of the watch. What connection could 

 there be between the arrangement of the atoms in the 

 molecule and the rotary power? 



Ill 

 PASTEUR: THE TARTRATES 



Such was the question which Pasteur must often have 

 put to himself, for it was at this juncture that he made 

 his appearance. Under Delafosse he had acquired the 

 taste for these researches, and as soon as he was out of 



