Nearly all medicines adminstered are received into the system by a process of absorption. Two great divisions of this function have been made: ist. The absorption of composition which obtains from without the organs, the material intended for the:r composition, its agents being the veins and chyliferous vessels. 2nd. The absorption of decomposition, which takes up from the organs the materials that have to be replaced* There is likewise an external pulmonary and cutaneous absorption that frequently demands the special attention of the practitioner.

*Prof. L. Hermann. †Dr. Richard Schneider. ‡Prof. H. C. Wood.

† Flint.

§Prof. Buchime.

To secure the therapeutic effects of the remedy much will depend on that adjusted physiological balance, with absorption on the one side and excretion on the other. A remedy of great force may be administered, but from slow absorption and rapid excretion, not attaining a sufficient amount of influence at any one time in the blood may produce little or no effect. This shows that the general action of a drug depends upon the presence of a certain amount of it in the blood, and that the amount circulating in the blood depends, not only on the amount administered, but upon the rapidity with which secretion takes place, † Previous to the absorption of a substance its solubility is effected by the aid of acids, alkalies, albuminoid substances, fatty matter, etc. As a rule, under a normal action, the more soluble the substance the more active the absorption. The solvent must be of a character to suit the nature of the substance to be absorbed. Some of the most important of these are the alkaline chlorides, albuminoid principles, and fatty matter, which aid in the introduction of certain metallic substances, soluble in albuminoid principles, or of phosphorus and sulphur solution in fatty matter.:}:

Bucham and Gad believe that the absorbability of cod-liver oil depends largely upon the presence of free fatty acid, but it is probably due to the biliary matter, since Dr. H. A. Hare finds it greatly increased by the addition of taurocholate and glycocholate of sodium. He asserts that cod-liver oil impregnated with a small quantity of the biliary salts is rapidly absorbed when rubbed upon the skin, and proposes the practical use of the mixture.§

Absorption in different localities varies in its energy, and some substances are more readily absorbed at one place than another.

Purgatives when active given by the stomach, show less effect when introduced by the rectum. On the other hand, a solution of opium, or extract of belladonna, or of strychnine is more readily absorbed through the rectum and the iliac S than by the stomach and the lesser intestines; because, when substances are retained so long in the stomach, and their absorption prevented for such a length of time, when they do reach the lesser intestine they are often therapeutically and chemically changed. By the alimentary canal iodoform is absorbed very slowly; from wounds it is taken up with comparative freedom. Iodol is absorbed slowly. This slow absorption is probably the reason that it is a less dangerous topical application than iodoform.§ Iodine itself is absorbed with considerable rapidity from the stomach, serous cavities, or the interior of cysts, and to some extent from the skin.*

*Robley Dunglison. ‡Prof. Adolph Gubler.

†Prof. L. Harmann. §Prof. H. C. Wood.

Pulmonary and subcutaneous absorption sometimes manifest an extraordinary and almost instantaneous energy, as in the inhalation of nitrite of amyl, and the hypodermic injection of the hydrochlorate of apomorphia, etc.

Gaseous or volatile substances are highly absorbable by the skin, and they are still more so when more decidedly gaseous, or under the form of volatilised substances. On the contrary, substances simply soluble in certain vehicles pass through the skin with comparative difficulty. When soluble in fatty bodies, they may penetrate to the superficial net-work and be absorbed. When dissolved in water absorption is almost impossible, or takes place very slowly. There is no absorption from baths; however when prolonged they give rise to alkaline urine. † A blistered surface will absorb wonderfully well. It is said that the oil of garlic may be absorbed from the skin as well as from the stomach.*

The absorbents of the skin can be better reached by constitutional means, than by external application; treatment of certain skin diseases establish this fact. In a few favorable cases the skin staining from nitrate of silver is said to have disappeared after the use of iodide of potassium and hyphosulphite of soda.*