The most favorable condition for continued and active absorption would be that in which the two liquids were kept in constant motion and incessantly renewed, so that the first one should never be exhausted of its materials, nor the second saturated with the substances-transmitted to it. If, at the same time, the intervening membrane maintained its freshness, unaltered by the changes of decomposition, the process of absorption would go on with the most continuous and uniform activity. These are precisely the conditions, in tact, which are present in the living body. In the alimentary canal, for instance, during digestion, there are constantly passing over the lining membrane of the intestine the nutritious fluids which have been extracted from the food. A portion of these are absorbed by the lining membrane; but, on the other hand, they are immediately taken up from it by the blood in its minute vessels. This blood, in the incessant movement of the circulation, is instantly carried away to another part of the body, its place being taken by other portions of the current following each other without intermission.

The living membranes themselves are maintained at the same time in their natural condition by the nutritive process, the temperature of the whole is constantly at or about 100° F., the superfluous materials are decomposed elsewhere, or discharged from the body by the excretory passages, and new supplies are incessantly furnished as the gradual digestion of the food is accomplished. - Experiments have shown that absorption will take place in the living-body with considerable rapidity even in nonvascular tissues, or where it is not directly assisted by the circulation of the blood. It has been shown by M. Gosselin that if a watery solution of iodide of potassium be dropped upon the cornea of a rabbit's eye, the iodine passes into the cornea, aqueous humor, iris, lens, sclerotic coat, and vitreous body, in the course of eleven minutes; that it will penetrate through the cornea into the aqueous humor in three minutes, and into the substance of the cornea in a minute and a half. In the vascular tissues, however, the rapidity of absorption is often much greater than this.

Thus the absorption of oxygen by the blood in the lungs is apparently instantaneous; the change of its color from blue to red, as soon as it arrives in the pulmonary vessels, showing the action of the gas which it has taken up from the atmosphere. This rapidity of absorption in the vascular tissues is due to the dissemination of the blood in a vast number of minute channels, by which the vascular and absorbing surfaces are brought into intimate contact over a large surface; and to the incessant motion of the fluid, by which its effect becomes perceptible at the earliest possible time. It is in some of the glandular organs that this ahsorption and reciprocal interchange of fluids has been shown to take place with the greatest activity; for the capillary blood vessels here form an exceedingly intricate and abundant network embracing the adjacent follicles and ducts of the glandular tissue, while these ducts and follicles themselves are arranged in a system of minute ramifying tubes and cavities, penetrating everywhere through the glandular substance.

Thus the union and interlacement of the glandular membrane on the one hand and of the blood vessels on the other becomes exceedingly extensive; and the ingredients of the blood are instantly subjected, over a very large surface, to the influence of the glandular membrane, or the fluids which it has absorbed. The rapidity of transudation under these conditions has been shown by the experiments of Claude Bernard and other observers. If a solution of iodide of potassium be injected into the duct of the parotid gland on one side, in a living animal, the saliva discharged by the corresponding gland on the opposite side is immediately afterward found to contain iodine. During the few instants required to perform this operation, therefore, the iodine in solution must have been taken up by the glandular membrane on one side, absorbed from it by the blood, carried by the blood to the heart, again distributed over the body, absorbed from the blood by the glandular membrane of the second gland, and thence discharged with the saliva. It is by this process that all the nutritious elements of the food and drink are taken up from the intestine and finally reach the tissues which they are to nourish.

They are absorbed from the cavity of the intestine first by its lining membrane; thence by the blood vessels and the blood contained in them; then transported by the circulation to the distant organs and tissues; and finally absorbed by these tissues from the blood, and united with their own substance. But as each tissue has a special power of its own of absorbing certain materials in preference to others, the same blood will supply its materials to each in different quantities. Thus the bones absorb from the blood a large proportion of calcareous matter, the cartilages a smaller quantity, and the muscles still less. The brain, on the other hand, takes up more water than the muscles, and the muscles more than the bones. Thus every tissue is enabled to maintain its own peculiar constitution, though all are supplied with the necessary ingredients from the same nutritious fluid. - It is now universally acknowledged that the action of drugs, medicines, and poisons takes place in the same way. This action is sometimes said to be local, as where the ingredients of a blister are absorbed by the skin and produce an inflammation of the integument at that spot only; or general, as Avbere opium when introduced into the stom-ach produces drowsiness or insensibility over the whole body.

But in both cases the process is essentially similar. The opium is dissolved by the liquids of the stomach, absorbed by its lining membrane, taken up by the blood, and distributed by the circulation all over the body. In this way reaching the brain, it is absorbed by the cerebral substance, and by its action upon the nervous matter causes the narcotism and insensibility which are manifested throughout the system. Thus the general action of an opiate is undoubtedly due to its local action upon the brain, and to the fact that the brain itself, through the nervous ramifications, influences the condition of the whole body.