When a substance in a soluble state is brought in contact with almost any part of the human body, internally as well as externally, more or less of it is taken into the general system by absorption. All parts are not equally active in absorption, neither can all parts be used with safety to the patient. The mucous surface is the 'most available part for the reception of medicines into the system. The absorbents of the serous membrane will admit medicines; but it can hardly ever be resorted to, owing to its great sensibility, and tendency to a violent dangerous inflammation when foreign bodies are brought in contact with it; this is in particular the case with the peritoneum.† The skin is frequently the seat of application by which medicines are administered, in the form of baths, unctions and under-clothing impregnated with medicine.† The skin is in remarkable contrast with the nature and function of the serous tissue; so blunt in its sensibility, that it is the place of selection for all powerful counter irritants. The skin being an emunctory, and subject to many forms of disease, may not only be treated topically, but constitutionally, the medicine often making its salutary impression in the process of elimination. Sulphur, arsenic, iodine, etc., become curative in many forms of cutaneous disease in this manner.

The place of application and avenue of introduction of a remedy are two things which are often confounded. A solution of benzoate of soda may be atomized, and inhaled, and absorbed into the system, and eliminated by the kidneys as hippuric acid.‡ The same solution may be taken into the stomach, or introduced into the rectum, with the same effect. Here we have an example of three imposing entrances of a substance into the system, leading to the kidneys.

Camphor may be absorbed from the mucous membrane from any point, to be eliminated by the lungs and the skin. When taken into the system by inhalation, it goes the rounds of the circulation, as if it had been taken into the stomach, and then eliminated at the point of introduction. There is no special rule to determine the avenues of introduction of medicines, except in their terminal physiological effects and process of elimination. Every drug of any perturbation has pretty much a route of its own in its transition through the system - Ave judge this to be so, from its effects.

*Prof. Rob. L. Edes.

†G. P. Hachenberg, M. D., on Important Points in Surgery, Cincinnati Medical News, Vol. IX., No. 9.

†G. P. Hachenberg, M. D., on Dermic Medication, Medical Record, 1877.

†G. P. Hachenberg, M. D., Under-clothing Impregnated with Medicines, Western Lancet, Vol. XIII.. p. 21.

‡Jaccoud.

The place and manner of application may be ever so varied. Iodoform is absorbed from the stomach, and so from any raw surface. Medical substances may be introduced in parenchymas, then again, in deep seated regions, as in deep seated cellular tissue of a limb, in the ganglions, and the thyroid .gland† - a system of treatment called the method of parenchymatous substitution.‡ But even in these instances, each remedy thus applied will follow its legitimate route through the system.

Chemical Alterations which Medicines Undergo.

A chemical change of a medicine may occur, even before its administration, through such influences as heat, light, moisture, and spontaneous decomposition. In the saccharated iodide of iron the addition of sugar is for the purpose of preserving the iodides from decomposition, but when exposed to sunlight the iodide is reduced to the condition of a subiodide.

When organic substances are introduced into the stomach, if there be considerable gastric activity, as for example, during the digestive process, they will meet with such important changes, that it may happen their effects will be greatly, if not entirely, impaired. You introduce aconite but obtain no results, not even with high doses. Atropine and morphine are subjected to the same destruction. Even quinine and the proximate alkaloids, which are so persistent, are not able to resist being modified, so that at meal time considerable quantities can be taken, without obtaining the desired result. In the stomach oxygen is also found. It has the effect of raising substances from a low to a higher degree of oxidation, which is what happens with sulphate or carbonate of protoxide of iron. It is converted into a sulphate of the peroxide of iron, which becomes basic. There is an ulterior oxidation, and a change to a higher condition. This free oxygen oxidizes all substances introduced, either at a low state of oxidation or absolutely free. Thus, if sulphurous acid is introduced, it has been suggested that it will be changed into sulphuric acid. When phosphorus is introduced into the stomach it passes to a higher degree of oxidation, and also undergoes other mutations due to the presence of water. Phosphorus decomposes water, and forms on the one hand phosphorus acid, and on the other phosphuretted hydrogen.* The hypophosphites probably all become oxidized in their passage through the alimentary canal. It is from the phosphites and not from the phosphates we derive the beneficial

†Laton.

*Prof. Adolph Gubler.

‡Gubler.

action of phosphorus in promoting healthy functions.†

Permanganate of potassium is supposed to act by oxidizing the blood.‡

When carbolic acid is taken in maximum doses, it is in part eliminated as carbolic acid, and the remainder of it in part escapes in combination with an alkali as sulphur-carbolic and glyco-uronic acids, and is in part oxidized in the system.§

Iodine seems to be eliminated, partly as an alkaline iodide and partly in organic combination.

Virchow says: "If we follow the chemical changes and action which iodide of potassium must necessarily undergo and exercise in its passage through the circulation, it is to be noted that it undergoes no change in the stomach, for whilst on the one hand, the extremely dilute hydrochloric acid of the gastric juice is incapable of decomposing it, so on the other it neither precipitates nor is decomposed by the albuminous compounds, sugar, starch, and salts, that are or may be present in that organ. It then enters the blood by diffusion in an altered state; but, even were the iodide decomposed by the hydrochloric acid of the gastric juice to some extent, it would only result in the entrance of hydriodic acid instead of iodide of potassium into the blood, the action of which would be similar. The large quantities of carbonic acid, which are continuously produced in the blood, will immediately act on the very dilute solution of the iodide in the blood, especially at the high pressure under which the gas exists in the blood. Hydriodic acid is set free with the formation of the bicarbonate of the alkali. The acid is, however, immediately broken into iodine and water. Thus, by the direct action of the oxygen of the blood upon the iodide of potassium, iodine must be set free.....the action of iodine depends, like that of bromine and chlorine, upon its affinity for hydrogen, which it displaces from the compound, and unites with to form free hydriodic acid. The molecule of hydrogen withdrawn from the compound, is at the same time, replaced by one of iodine; but this new compound, being unstable, immediately breaks up, and the secondary products readily undergo oxidation. In the same way the hydriodic acid dissolving in the blood, itself undergoes oxidation, and the iodine is again set free to pass through the series of changes. A single molecule of iodine may thus aid in the decomposition of many molecules of organic matter, which explains the action of small doses of it."

The sulphite of potassium is in part decomposed when introduced into the blood; it is excreted, in part, in the state of sulphate of potas-sa, that is, the sulphur has become sulphuric acid, and, in this state, has induced the formation of sulphate of potassa, which is thus excreted in the urine.* Tannic acid splits up into gallic acid and glycol; it simply takes up water to add the necessary quantity of hydrogen and

†Thomas S. Mays.

‡Waring.

§Prof. H. C. Wood.

||Prof. See.

oxygen to that which is already contained. All essential oils which are resinified, and which passing to the state of oxides, combine with the acids and become true salts, and will pass in large part by the urinary passages. *

When nitrate of silver is mixed with bread crumbs, or bread in the stomach, in a very few moments the silver is reduced and chloride or albuminate of silver is formed. More than seven-eighths of the nitrate of silver is thus decomposed into metallic silver. The soluble salts introduced into the primae viae where they meet with chloride of sodium, form insoluble salts - the organic salts combine with potassa or soda, so when citric acid is administered, carbonate of soda is eliminated from the kidneys.

As a consequence of the action of the pancreatic juice, salol splits up into carbolic and salicylic acids, which are then eliminated by the kidneys, carbolic acid without being changed, salicylic acid after combining with sodium. Nencki, Sahli, and Lepine have as a consequence recommended its internal use in "internal disinfection" in cholera, typhoid fever, and bacterial diseases.