This section is from the book "Botanic Drugs Their Materia Medica, Pharmacology and Therapeutics", by Thomas S. Blair. Also available from Amazon: Botanic Drugs, Their Materia Medica, Pharmacology and Therapeutics.
But there are many difficulties as regards the graphic formulae of the salicyl and benzoyl compounds. From this point of view, salicylic acid is an ortho-oxybenzoic acid, and assuredly so as prepared from wintergreen. Now three oxybenzoic acids are known, differing in the relative positions of their side claims - ortho, meta, and para oxybenzoic acids. Only the first is really active, the other two having feeble actions. Salicylic acid has two side chains, and there are few agents in the materia medica offering similar opportunities for the making of new products by substituting various groups in one or other, or both, side chains hung on the salicyl ion. The synthetic chemist can make innumerable compounds of the salicyl ion, giving their chemical formulae accurately and a theoretic graphic formula of each. That is as far as he can go. Graphic formulae are easy to construct, but hard to prove or disprove.
I can set up the contention that the graphic formulae of the natural and the synthetic salicylic acids are not similar, but I can't prove it; and the synthetic chemist may claim the opposite, and have considerable difficulty to prove the argument. But we do know that atropine, hyoscyamine, and hyoscine have the same formula (C17H23NO3) given for them in some texts, but differing graphic formulae. But the chemist meets this with the explanation of "racemisation." Now atropine (or hyoscyamine) consists of a basic nucleus called tropine, which is, by the way, quite similar to the ecgonine nucleus of cocaine, united to a radicle of tropic acid. And this same chemist may assert that the formula of hyoscine is C17H21NO4 (sometimes stated C17H21O4N) because it is identical with scopolamine. But, lo and behold, that is the formula given for cocaine! So where are we?
Now jump over to the synthetic side and we find nearest cocaine is novocaine (CH2(C6H4NH2-COO). CH2[N(C2H5)2]HC1), or simplified to C13H20-O2N2HC1. This is the way it is all along the line. I predict that ultimately we will find out the same difficulty inheres in natural and synthetic salicylic acids and their formulae.
Furthermore, the pharmacology of salicylic acid does not at all account for its action in acute rheumatic fever, where it is nearly specific. With this fact in view, it is hard to confidently assert that the synthetic salt is as efficacious and safe in the treatment of rheumatism as is the natural acid except purely upon a basis of clinical experience.
The controversy for and against the claims made for the natural acid has waxed hot; but in view of what has been stated, how are we to determine the matter except by clinical experience? In this gentlemen will differ, and differ honestly.
This author has used both the natural and the synthetic products in the treatment of a great many cases of rheumatism; and there has never been trouble under the administration of the natural acid, whereas sometimes there has been with the synthetic acid. One can't determine this matter on the basis of a few cases. Case after case will do well on the synthetic acid, and then one goes wrong, perhaps because the product was impure. One does not have to look out for these impurities when employing the natural acid.
But I have had trouble with the synthetic acid in cases where the product employed was of the highest grade obtainable and taken direct from original packages. The cases where the synthetic acid produced irritation and other unpleasant effects were those wherein the temperature was high.
So I am using the natural acid, not from any prejudice in the matter, but because it has worked out better in practice and relieves me of worries when full doses in hyperpyrexia are necessary. Many clinicians feel as I do in the matter, and others do not; but I feel that my attitude is the safe one. If I encounter trouble with the natural acid and its salts, I may change my mind; but I have used it satisfactorily in so many cases that I feel the advocates of the natural products have, thus far, the practical side in the argument; and I have introduced the matter here because this is a special work on botanic drugs, and wherein I believe them to be preferable to the synthetics I wish to tell why I so believe.
Salicylic acid is an antiseptic, a protoplasmic poison to the lower organisms. It checks fermentation, but has little penetrating power. It is rapidly absorbed, producing cutaneous vasodilation, profuse perspiration, slightly accelerated respiration, and an evanescent rise in blood-pressure. Large doses produce "salicylism," which is akin to "cinchonism." Still larger doses cause depression of the medullary centers without convulsions. Medicinal doses slightly accelerate the heart action and increase the flow of bile. Nitrogenous metabolism is stimulated, and excretion is by the kidneys. It circulates in the blood as an alkaline salt. The alkaline salts are decomposed in the stomach.