ADDRESS. cm 



childish ; hut from mechanics let us pass on to chemistry, and the case will bo 

 found by no means so clear. When chemists ceased to be content ^vith the 

 mere ultimate analysis of organic substances, and set themselves to study 

 their proximate constituents, a great number of definite chemical compoiinds 

 •were obtained which could not be formed artificially. I do not know what 

 may have been the usual opinion at that time among chemists as to their 

 mode of formation. Probably it may have been imagined that chemical 

 affinities were indeed concerned in their formation, but controlled and modi- 

 fied by an assumed vital force. But as the science progressed many of these 

 organic substances were formed artificially, in some cases from other and 

 perfectly distinct organic substances, in other cases actually from their ele- 

 ments. This statement must indeed be accepted with one qualification. It 

 was stated several years ago by M. Pasteur, and I believe the statement 

 still remains true, that no substance the solution of which possesses the pro- 

 perty of rotating the plane of polarization of polarized light had been formed 

 artificially from substances not possessing that property. Now several of the 

 natural substances which are deemed to have been produced artificially are 

 active, in the sense of rotating the plane of polarization ; and therefore in 

 these cases the inactive, artificial substances cannot be absolutely identical 

 with the natural ones. But the inactivity of the artificial substance is 

 readily explained on the supposition that the artificial substance bears to the 

 natural, the same relation as racemic acid bears to tartaric, — that it is, so to 

 speak, a mixture of the natural substance with its image in a mirror. And 

 when we remember by what a peculiar and troublesome process M. Pasteur 

 succeeded in separating racemic acid into the right-handed and left-handed 

 tartaric acids, it will be at once understood how easily the fact, if it be a 

 fact, of the existence in the natural substance of a mixture of two substances, 

 one right-handed and the other left-handed, but otherwise identical, may 

 have escaped detection. This is a curious point, to the clearing up of which 

 it is desirable that chemists should direct their attention. Waiving then tho 

 difference of activity or inactivity, which, as we have seen, admits of a simple 

 physical explanation, though the correctness of that explanation remains to 

 be investigated, we may say that at the present time a considerable number 

 of what used to be regarded as essentially natural organic substances have 

 been formed in the laboratory. That being the case, it seems most reason- 

 able to suppose that in the plant or animal from which those organic sub- 

 stances were obtained they were formed by the play of ordinary chemical 

 affinity, not necessarily nor probably by the same series of reactions by 

 which they were formed in the laboratory, where a high temperatm-e is com- 

 monly employed, but still by chemical reactions of some kind, under the agency 

 in many cases of light, an agency sometimes employed by the chemist in his 

 laboratory. And since the boundary line between the natural substances 

 which have and those which have not been formed artificially is one which, 

 so far as we know, simply depends upon the amount of our knowledge, and 

 is continually changing as new processes are discovered, we are led to extend 

 the same reasoning to the various chemical substances of which organic 

 structures are made up. 



But do the laws of chemical affinity, to which, as T have endeavoured to infer, 

 living beings, whether vegetable or animal, are in absolute subjection, together 

 with those of capillary attraction, of diffusion,and so forth, account for the for- 

 mation of an organic structure, as distinguished from the elaboration of the che- 

 mical substances of which it is composed ? No more, it seems to me, than the 

 laws of motion account for the union of oxygen and hydrogen to form water 



