228 Dr. a Meymott Tidy [March 2, 



or atroj)me, or quinine, or veratrine (none of which bodies arc com- 

 parable in their physiological action to strychnine), and convert 

 them into their methyl derivatives, the methyl compounds formed 

 (viz. methyl-morphine, methyl-nicotine, &c.) are comparable in their 

 physiological action to methyl-strychnine. 



We must admit these experiments to be striking. One treasures 

 any ex23eriment suggestive of the chemical constitution of a body 

 indicating physiological action. 



But again: — The true physiological action of a drug is not so 

 much its general as its selective action, this selective action being 

 largely dependent on the dose administered and the mode of 

 administration. 



For example : Inject into the circulation of a frog a small dose 

 of veratrine, great muscular stiffness results, a large dose similarly 

 administered not producing this effect. And now change the method 

 of administration : Apply the small dose directly to the muscle, you 

 get no symptom ; but apply the large dose directly, and great muscular 

 stiff'ness results. Here see the modifying influence of dose and of the 

 mode of administration. 



Again, the difficulty of " allotropism " in the case of elements, 

 finds its counterpart in " isomerism " in the case of compounds. 

 Thus cyanogen and paracyanogen are bodies of identical percentage 

 composition, and yet cyanogen is one of the most poisonous of gases, 

 whilst paracyanogen is one of the most inert of solids. 



Or, again, take piperin and morphine. These bodies are of identical 

 percentage and molecular composition. They agree (it is true) in 

 being poisons. But how vastly different their physiological action ! 

 — the one an extreme irritant, the other a powerful narcotic. 



I fear we must admit that, as no a priori reasoning could predict 

 that by combining copper and sulphuric acid a blue salt would be 

 formed, so no a priori reasoning, no knowledge of chemical constitu- 

 tion, can predicate what will be the special organ on which any 

 given poison will act, nor, even supposing that the organ upon which 

 the chemical activity of the drug will be exerted be known, what will 

 be the nature of such chemical action. The science of drugs, like 

 the science of chemistry, is, and must ever remain, an experimental 

 science. 



And, be it remembered, the poisons of the toxicologist are the 

 medicines of the physician. Physiological action is a subject-matter 

 for experiment. Let the guard be jealously set and as rigidly 

 maintained to prevent cruelty to animals ; but ask yourselves, whether 

 to rob the higher creation of life and health rather than that one of 

 the lower creation should suffer, be not a refinement of cruelty — the 

 cruelty of cruelties ? " Are ye not of much greater value than they ? " 

 speaks a still small voice amidst the noisy babble of well-intentioned 

 enthusiasts. 



Two general observations are suggested. And this first : The 

 later age history of poisoning is the history of a profession. This 



