TO THE NERVOUS MATTER. 187 



in both cases) is absolutely incapable of yielding 

 blood ; if, therefore, nitrogenised compounds, to- 

 tally different from the compounds of proteine, may 

 be employed for purposes corresponding to their 

 composition ; we may thence conclude that a product 

 of vegetable life, also different from proteine, but 

 similar to a constituent of the animal body, may be 

 employed by the organism in the same way and for 

 the same purpose as the natural product, originally 

 formed by the vital energy of the animal organs, 

 and that, indeed, from a vegetable substance. 



The time is not long gone by, when we had not 

 the very slightest conception of the cause of the vari- 

 ous effects of opium, and when the action of cinchona 

 bark was shrouded in incomprehensible obscurity. 

 Now that we know that these effects are caused by 

 crystallizable compounds, which differ as much in 

 composition as in their action on the system ; now 

 that we know the substances to which the medi- 

 cinal or poisonous energy must be ascribed, it would 

 argue only want of sense to consider the action of 

 these substances inexplicable ; and to do so, as 

 many have done, because they act in very minute 

 doses, is as unreasonable as it would be to judge of 

 the sharpness of a razor by its weight. 



94. It would serve no purpose to give these con- 

 siderations a greater extension at present. How- 

 ever hypothetical they may appear, they only de- 

 serve attention in so far as they point out the way 

 which chemistry pursues, and which she ought not 



