18 LOUIS PASTEUR. 



properties that is to say, a tartaric acid possessing, 

 like the natural tartaric acid of the grape, dissymmetry 

 of form, and exerting an action on polarised light. 

 Per contra, I ought to be able to extract from the 

 second sort of crystals, associated with the former in 

 the paratartaric group, an acid which will reproduce 

 ordinary tartaric acid, but possessing a dissymmetry 

 of an inverse kind and exerting an action equally in- 

 verse on polarised light. 



With a feverish ardour Pasteur hastened to make 

 this double experiment. Imagine his joy when he 

 saw his anticipations not only realised but realised 

 with an exactitude truly mathematical. His delight 

 was so great that he quitted the laboratory abruptly. 

 Hardly had he gone out when he met the assistant of 

 the physical professor. He embraced him, exclaim- 

 ing, ' My dear Monsieur Bertrand, I have just made a 

 great discovery ! I have separated the double para- 

 tartrate of soda and ammonia into two salts of inverse 

 dissymmetry, and exerting an inverse action on the 

 plane of polarisation of light. I am so happy that a 

 nervous tremulousness has taken possession of me, 

 \vhich prevents me from looking again through the 

 polariscope. Let us go to the Luxembourg, and I will 

 explain it all to you.' 



These results excited in a high degree the attention 

 of the Academy of Sciences, where sat, at the time now 

 referred to, Arago, Biot, Dumas, De Senarmont, and 



