178 LOUIS PASTEUR, 



previously extracted from the two tartrates acids which, 

 in regard to polarised light, behaved like themselves. 

 Such was the worthy opening of M. Pasteur's scientific 

 career, which has been dwelt upon so frequently and 

 emphatically by M. Kadot. The wonder however is, 

 not that a searcher of such penetration as Pasteur 

 should have discovered the facets of the tartrates, but 

 that an investigator so powerful and experienced as 

 Mitscherlich should have missed them. 



The idea of molecular dissymmetry, introduced by 

 Biot, was forced upon Biot's mind by the discovery of a 

 number of liquids, and of some vapours, which possessed 

 the rotatory power. Some, moreover, turned the plane 

 of polarisation to the right, others to the left. Crystal- 

 line structure being here out of the question, the notion 

 of dissymmetry, derived from the crystal, was trans- 

 ferred to the molecule. " To produce any such phe- 

 nomena," says Sir John Herschel, " the individual mole- 

 cule must be conceived as unsymmetrically constituted." 

 The illustrations employed by M. Pasteur to elucidate 

 this subject, though well calculated to give a general idea 

 of dissymmetry, will, I fear, render but little aid to the 

 reader in his attempts to realise molecular dissymmetry. 

 Should difficulty be encountered here at the threshold 

 of this work, I would recommend the reader not to be 

 daunted by it, or prevented by it from going further. 

 He may comfort himself by the assurance that the con- 

 ception of a dissymmetric molecule is not a very precise 

 one, even in the mind of M. Pasteur. 



One word more with regard to the parentage of 

 preconceived ideas. M. Eadot informs us that at 

 Strasburg M. Pasteur invoked the aid of helices and 

 magnets, with a view to rendering crystals dissym- 

 metrical at the moment of their formation. There 

 can, I think, be but little doubt that such experiments 



