XVL11 INTRODUCTION. 



able to produce in the laboratory, by the ordinary 

 processes of chemistry, a dissymmetric molecule in 

 other words, a substance which, in a state of solution, 

 where molecular forces are paramount, has the power 

 of causing a polarised beam to rotate. This power 

 belongs exclusively to derivatives from the living world. 

 Dissymmetric/orccs, different from those of the labora- 

 tory, are, in Pasteur's mind, the agents of vitality ; it is 

 they that build up dissymmetric molecules which baffle 

 the chemist when he attempts to reproduce them. Such 

 molecules trace their ancestry to life alone. ' Pour- 

 rait-on indiquer une separation plus profonde entre les 

 produits de la nature vivante, et ceux de la nature 

 minerale, que cette dissymmetric chez les uns, et son 

 absence chez les autres ? ' It may be worth calling 

 to mind that molecular dissymmetry is the idea, or 

 inference, the observed rotation of the plane of polari- 

 sation, by masses of sensible magnitude, being the fact 

 on which the inference is based. 



That the molecule, or unit brick, of an organism 

 should be different from the molecule of a mineral is 

 only to be expected, for otherwise the profound dis- 

 tinction between them would disappear. And that 

 one of the differences between the two classes of 

 molecules should be the possession, by the one, of 

 this power of rotation, and its non-possession by the 

 other, would be a fact, interesting no doubt, but not 

 surprising. The critical point here has reference to 



