224 ON VARIABILITY AND ADAPTATION 



member that difference in chemical constitution means difference 

 in the readiness with which the elements separate and reunite 

 and release their energy. Remember also that minute differences 

 in constitution enable these chemical compounds then to blend 

 with the vital action in one structure, or to be absolutely inert. 

 It must depend on differences in the vital chemistry which 

 underlies function, although these differences which determine 

 affinity or indifference we can discern only by the result. 



" Nerve force, as far as we can see, is the result of chemical 

 change occurring under the influence of life in the molecules 

 which compose nerve tissue. Chemical processes, the breaking 

 up of complex compounds, and the formation of simpler com- 

 pounds, with consequent release of the energy held latent in the 

 Jformer, is the constant element in the production and conduction 

 of nerve impulses. Some chemical compounds may come into 

 relation with the tissue in which the change is occurring without 

 exerting the slightest influence upon it. But another substance 

 may come even in amount inconceivably minute, whose molecules 

 are so arranged as to fit, as it were, with the changing molecules 

 of the living tissue. The energy the new molecules bear seems 

 to blend with that which is in process of ordered release in the 

 living tissue, and to blend so effectively as to derange it entirely. 

 Such an influence as I have spoken of seems to be exerted widely 

 in the case of aconitia. Its contact with some living nerve 

 structures seems to be so instant and precise as to induce the 

 production of an excess of energy, sweeping all before it ; on 

 others, to oppose the process, to induce a sudden stillness among 

 the changing molecules, and to arrest all action. Among the 

 nerves thus influenced may be those on which depend the action 

 of the heart, and with a sudden spasm or a sudden stillness, the 

 heart stops and life is ended." 



I have quoted these last three paragraphs from a clinical 

 lecture delivered several years ago by Sir William Gowers. I 

 have not altered his words ; they approach near enough to what 

 I wish to impress upon you to serve my purpose. They lay down 

 in a striking manner that the sole difference that we can determine, 

 from a chemical point of view, between the living, palpitating 

 matter and protein, between " imperial Caesar " and his own 

 dead " clay," is brought about by chemical combination, by 

 the entrance of certain molecules into combination with the 



