The Action of Medicines in the System / Or, on the mode in which therapeutic agents introduced into the stomach produce their peculiar effects on the animal economy

by Frederick William Headland

(Mineral:—Sulphuric, Hydrochloric, Nitric, and Phosphoric Acids. Vegetable:—Acetic, Citric, Tartaric, and Malic Acids.)

To this list may be added the super-salts of the alkalies, which have an acid reaction.

Although the mineral differ from the vegetable acids in their ultimate action, and are altogether more powerful than them, yet in their proximate effects they are similar. They are all soluble in water, and, when given as medicines, should be so diluted that they can exert no corrosive action on the mucous coat of the stomach and intestines.

Dr. Pereira lays it down as an axiom that though they all act as acids in the alimentary canal, yet that they enter the blood as salts. He considers that they combine with free alkaline matters in the saliva, bile, and Pancreatic juice. (Materia Medica, vol. i. p. 171.)

But this explanation seems to me to be calculated to communicate an erroneous idea of their action. For supposing first that they did thus combine with alkalies before entering the blood, yet as more alkaline matter would then have to be secreted to supply that which they had neutralized, they would thus immediately increase the amount of acid in that fluid. The action of acids in the blood is very different from that of their salts. Sulphuric acid does not act like the sulphates of Soda and Magnesia, nor is the action of Hydrochloric acid the same as that of common salt. Again, we must remember that the secretions mentioned are either neutral or barely alkaline in their reaction, and that the acid medicine, on passing into the stomach, would meet there with an active absorbent surface, secreting an acid, and not an alkaline fluid. So that it seems probable that the acid would enter the blood as such.

Now the presence of the acid is not unnatural to the blood. The mineral acids exist there in combination, and the vegetable acids have an analogue in lactic acid.

The blood is alkaline; which is due either to the presence of carbonate of Soda, or (according to Liebig) of an alkaline phosphate of that base. So that the acid, on entering into the blood, passes at once into combination with this alkali, and the result of this is a general diminution of the amount of basic matter in the system, and an increase in that of acid. Thus a free acid may act as a Restorative in cases where there is an excess of alkali in the blood. It may either remain in the blood after entering into combination, or it may pass off by the urine, supplying there the place of a natural acid, which it leaves behind it in the system. It is on such a theory as this that the action of mineral acids in typhoid and putrid fevers has been explained. I do not mean to affirm positively that there is in these cases an excess of alkali in the blood. Although likely, it is not proved. The explanation is plausible.

Acids are used to correct a phosphatic deposit in the urine, caused by an alkalinity of that secretion. The alkaline urine may be secreted so, as has been observed in petechial fever by Dr. Graves and Dr. Golding Bird, and in insanity by Dr. Sutherland, and may also occur in diseases of the nervous centres; or it may be caused by a decomposition taking place in the bladder, as in chronic inflammation, or in the case of retention of urine from any cause. In the former case the acid may act as a corrective to the fluids before secretion; in the latter case, after it. But it is not always easy to cause acidity of the urine by any medicines. Mineral acids may be excreted in other ways, and vegetable acids are liable to decomposition in the system. (Vide page 125.)

The use of mineral acids in assisting a weak digestion admits of a simple explanation. For whatever notion we adopt as to the composition of the gastric juice, it is certain that it contains an acid in excess. Now an acid medicine would set free in the blood more of this acid which it is the business of the stomach to furnish, and thus prove useful in that kind of dyspepsia which depends on a failure of the gastric secretion. Hydrochloric acid has been particularly recommended by those who consider it to be the acid normally secreted by the stomach.