26 * THE LIFE OF PASTEUR 



the thick crusty formations within wine barrels called " tar- 

 tar "; but the latter was disconcerting to chemists. In 1820 

 an Alsatian manufacturer, Kestner, had obtained by chance, 

 whilst preparing tartaric acid in his factory at Thann, a very 

 singular acid which he was unable to reproduce in spite of 

 various attempts, fie had kept some of it in stock. Gay- 

 Lussac, having visited the Thann factory in 1826, studied this 

 mysterious acid ; he proposed to call it racemic acid. Berzelius 

 studied it in his turn, and preferred to call it paratartaric . 

 Either name may be adopted ; it is exactly the same thing : 

 men of letters or in society are equally frightened by the word 

 paratartaric or racemic. Chappuis certainly was when Pasteur 

 repeated to him word for word a paragraph by a Berlin chemist 

 and crystallographer named Mitscherlich. Pasteur had pon- 

 dered over this paragraph until he knew it by heart ; often 

 indeed, absorbed in reading the reports for 1844 of the 

 Academic des Sciences, in the dark room which was then the 

 library of the Ecole Normale, he had wondered if it were pos- 

 sible to get over a difficulty which seemed insurmountable to 

 scientists such as Mitscherlich and Biot. This paragraph 

 related to two saline combinations tartrate and paratartrate 

 of soda or ammonia and may be epitomized as follows : in 

 these two substances of similar crystalline form, the nature and 

 number of the atoms, their arrangement and distances are the 

 same. Yet dissolved tartrate rotates the plane of polarized 

 light and paratartrate remains inactive. 



Pasteur had the gift of making scientific problems interest- 

 ing in a few words , even to minds least inclined to that particii- 

 lar line of thought. He rendered his listener's attention very 

 easy ; no question surprised him and he never smiled at ignor- 

 ance. Though Chappuis, absorbed in the series of lectures on 

 philosophy given at that time by Jules Simon, was deep in a 

 train of thought very far away from Mitscherlich 's perplexities, 

 he gradually became interested in this optical inactivity of para- 

 tartrate, which so visibly affected his friend. Pasteur liked to 

 look back into the history of things, giving in this way a 

 veritable life to his explanations. Thus, a propos of the optical 

 phenomenon which puzzled Mitscherlich, Pasteur was speak- 

 ing to his friend of crystallized carbonate of lime, called Iceland 

 spar, which presents a double refraction that is 'to say : if you 

 look at an object through this crystal, you perceive two repro- 

 ductions of that object. In describing this, Pasteur was not 



