MOLECUL,\R DISSl'lMMETRY 27 



only in very exceptional positions that compensa- 

 tions like those which we have just pointed out 

 could occur, and, without being able to indicate in 

 detail the results or the direction of the general resultant, 

 we see, nevertheless, that the total effect could not be 

 the same as in the first case. The path of the ray of 

 polarized light where the direction of the vibration 

 is constant and unique must depend on the direction 

 in which the obstacles it encounters are placed. With 

 out going into this problem further, it is possible to admit 

 that the deviation of the plane of polarization depends 

 on the manner of distribution of the obstacles, and that, 

 according as the dissymmetry in the atoms is right or 

 left there will be a right or a left rotation. 



Of less importance is the mechanism of the action, 

 which always remains a little hypothetical. It is suffi- 

 cient that the experimental study of the tartrates has 

 linked indissolubly these two ideas: the molecular rotary 

 power, and the dissymmetry of the molecule. This 

 suffices to give us the right to attribute dissymmetrical 

 molecules to all substances acting in solution on polar- 

 ized light, and when one considers that all these sub- 

 stances belong to the vegetable or animal kingdom, 

 that is to say, are the products of cellular activity, 

 this pecuharity of structure becomes curious, if regarded 

 closely. Guided by an imagination at once so adven- 

 turous and so well controlled as was that of Pasteur, 

 we are constantly on the border of new countries, but we 

 journey with security. 



