LOUIS PASTEUR. 231 



suggests, probably bearing in mind the properties of rock 

 crystal, and the difference of the facets in the right- and 

 left-handed crystals, he saw reason in Mitscherlich's note 

 to the Academy of Sciences — that tartrates of soda and 

 ammonia caused the plane of polarised light to rotate to 

 the right, whilst the paratartrate, which in chemical com- 

 position is absolutely the same, causes no rotation — to make 

 a careful search for facets like those that had already been 

 found to exist in rock crystal. Such facets he was 

 able to find in the tartrates, and this being done he 

 assumed that the want of power of rotating light which 

 existed in the paratartrate must be due to the combination 

 of the opposite rotating powers of right- and left-handed 

 crystals. He anticipated, indeed, that the tartrate was 

 without a plane of symmetry, whilst the paratartrate 

 was symmetrical, and that the crystals of the paratartrate 

 would be all characterised by the absence of dissymmetry ; 

 on coming to examine the crystals carefully he found, 

 however, that certain of them were dissymmetrical in 

 one way, others in an opposite. " Some of these crystals 

 when placed before a mirror produced the image of 

 the others, and one of the two kinds of crystals cor- 

 responded rigorously in form to the tartrate prepared by 

 means of the tartaric acid of the grape," and he argued that 

 one of these forms of crystals must therefore be the one 

 found in the right-handed tartrate, whilst the other must 

 be something different, and he undertook the laborious 

 task of separating the different kinds of tartrate crystals, 

 placing them in two groups : those like the ordinary right- 

 handed tartrate, and those which he found rotated light to 

 the left. These experiments were carried out during his 

 final year of study in the Ecole Normale where he took 

 his Doctorate in 1847, during the time that he was Pro- 

 fessor of Physical Science in the Lycee of Dijon, and whilst 

 he was acting as Assistant Professor of Chemistry in the 

 University of Strasburg. (It was in Strasburg that 

 Pasteur met his future wife — Mcllle. Marie Laurent.) 



As a result of these physical and chemical observations 

 Pasteur conceived the idea that there was an essential differ- 



