within it. He then placed the vein in a slightly acid liquor, and carefully collected the fluid of the current. During the first few minutes, the fluid exhibited no change; but, in five or six minutes, it became sensibly acid. This experiment was repeated on veins taken from the human subject, with the same results; and not only with veins but with arteries. Similar experiments were next made on living animals. He took a young dog, about six weeks old, whose vessels were thin, and, consequently, best adapted for the success of the experiment, and exposed one of its jugular veins. This he dissected entirely from surrounding matter, and especially from the cellular tissue and the minute vessels, that ramified upon it, and placed it upon a card in order that there might be no point of contact between it and the surrounding parts. He then let fall upon its surface and opposite the middle of the card, a thick, watery solution of nux vomica,—a substance, which exerts a powerful action upon dogs. He took care that no particle of the poison touched any thing but the vein and card, and that the course of the blood, within the vessel, was free. Before the end of three minutes, the effects, which he expected, appeared, at first feebly, but afterwards with so much activity, that he had to prevent fatal results by inflating the lungs.

The experiment was repeated on an older animal with the same effects; except that, as might be expected, they were longer in exhibiting themselves, owing to the greater thickness of the parietes of the veins.

Satisfied, as regarded the veins, he now directed his attention to the arteries; and with like results. They were, however, slower in appearing than in the case of the veins, owing to the tissue of the arteries being less spongy than that of the veins. It required more than a quarter of an hour for imbibition to be accomplished.

In one of the rabbits, which died under the experiment, they had an opportunity of discovering, that the absorption could not have been effected by any small veins, that had escaped dissection. One of the carotids—the subject vessel of the experiment—was taken from the body; when the small quantity of blood, adherent to its inner surface, was found by Magendie, and his friends who assisted at the experiment, possessing the extreme bitterness, which characterizes the nux vomica.

These experiments were sufficient to prove the fact of imbibition by the large vessels, both in the dead and the living state. His attention was now directed to the small vessels, which seemed, a priori, favourable to the same action, from their delicacy of organization. He took the heart of a dog, which had died the day before; and injected, into one of the coronary arteries, water at the temperature of 86° of Fah. The water readily returned by the coronary vein into the right auricle, whence it was allowed to flow into a vessel. Half an ounce of water, slightly acidulated, was now placed in the pericardium. At first, the injected fluid did not exhibit any

signs of acidity; but, in five or six minutes, the evidences of it were unequivocal.

From these facts, Magendie draws the too exclusive deduction, that "all blood-vessels, arterial and venous, dead or living, large or small, possess a physical property, capable of perfectly accounting for the principal phenomena of absorption." We shall endeavour to show, that it explains only certain varieties of absorption,those in which the vessel receives the fluid unmodified, but that it is unable to account for absorptions, in which an action of selection and elaboration is necessary.

Since these experiments were performed others have been instituted by MM. Segalas and Fodera; from which the latter physiologist attempts to show, that exhalation is, simply, transudation of substances from the interior of vessels to the exterior; and that absorption is imbibition, or the passage of fluids from the exterior to the interior. The facts, adduced by Fodera in support of his views, will be considered under the head of secretion. They chiefly go to show the facility with which substances penetrate the different vascular parietes and other tissues of the body; an action, which he found to be singularly accelerated by the galvanic influence. Some prussiate of potassa was injected into the cavity of the pleura; and sulphate of iron was introduced into the abdomen of a living animal. Under ordinary circumstances, it requires five or six minutes, before the two substances meet by imbibition through the diaphragm; but the admixture is instantaneous if the diaphragm be subjected to a slight galvanic current. The same fact is observed, if one of the liquids be placed in the urinary bladder, and the other in the abdomen; or the one in the lung, and the other in the cavity of the pleura. It was farther found, that, according to the direction of the current, the union took place in one or other cavity.

Dr. Bostock, in commenting on these cases, thinks it must be admitted, that they "go very far to prove that membranes, perhaps, even during life, and certainly after death, before their texture is visibly altered, have the power of permitting the transudation of certain fluids." That such imbibition occurs during life, appears to us indisputably proved. If the clear and decisive experiments of Magendie and Fodera do not establish it; the additional testimony,—afforded by Lawrence, Coates and Harlan; by Dutrochet, Togno, Mitchell and others,— commands it. By the different rates of penetrativeness of different fluids, and of permeability of different tissues, as exhibited in the essays of the last gentleman, we can explain, why imbibition may occur in one set of vessels and not in another; and why there may not be the same tendency to transude from the vessel, after they have entered it by imbibition, as has been suggested by Dr. Bostock; indeed, the constant current, established in the interior of the vessel, would be a sufficient reply to this suggestion.

ADELON, again, affirms, that we ought, under the view of imbibition, to find imbibed substances in the arteries and lymphatics, also. A sufficient objection to this would be,—the comparative tardiness, with which the former admit of the action, and the selection, and, consequently, refusal, exerted by the latter; but even here we occasionally find evidences of adventitious imbibition; as in the case of salts, that have been detected in the thoracic duct, when introduced into the cavity of the abdomen.

The two following experiments of Dr. Mitchell, which are analogous to numerous others, that have been performed, in the investigation of this subject, ratify the fact of imbibition in the living tissues.

A quantity of a solution of acetate of lead was thrown into the peritoneal cavity of a young cat; and sulphuretted hydrogen was passed, at the same time, into the rectum. In four minutes, the

poisonous gas killed the animal. Instantly on its death, the peritoneal coat of the intestines, and the parietes of the cavity in contact with them were found lined with a metallic precipitate, which adhered to the surface, and was removable by nitric acid, moderately diluted. It was the characteristic precipitate of sulphuretted hydrogen, when acting on lead.

In another experiment on a cat, a solution of acetate of lead was placed in the thorax, and sulphuretted hydrogen in the abdomen. Almost immediately after the entrance of the sulphuretted hydrogen into the abdominal cavity, death ensued. On inspecting the thoracic side of the diaphragm, which was done as quickly as possible, the tendinous part of it exhibited the leaden appearance of the precipitate by sulphuretted hydrogen.

It may be concluded, then, that all the living tissues imbibe the liquid matters which come in contact with them; and that the same occurs to solid matters, provided they are soluble in the humours, and especially in the serum of the blood.

Within the last few years, Dr. Barry,—in different memoirs laid before the Académie Royale de Médecine, the Académie Royale des Sciences of Paris, and the Medico-Chirurgical Society of London, has maintained, that the whole function of external absorption is a physical effect of atmospheric pressure; and "that the circulation, in the absorbing vessels and in the great veins, depends upon this same cause, in all animals possessing the power of contracting and dilating a cavity, around that point, to which the centripetal current of their circulation is directed." In other words, it is the opinion of this gentleman, that, at the time of inspiration, a tendency to a vacuum is produced in the chest by its expansion; and as the atmospheric pressure, externally, thus ceases to be counterbalanced, the pressure without occasions the flow of blood towards the heart, along the veins.

The consideration of the forces, that propel the blood, will afford us an opportunity of saying a few words on this view; at present, VOL. II.

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we will only observe, that he ascribes absorption,—which he explicitly states to be, in his opinion, extra vital—to the same cause. In proof of this, he instituted numerous experiments, in which the absorption of poisons from wounds appeared to take place or to be suspended, according as the wounds continued, as he conceived, exposed to atmospheric pressure, or were freed from its influence by the application of a cupping-glass. The same quantity of poison, which, under ordinary circumstances, destroyed an animal in a few seconds, was rendered completely innocuous by the exhausted vessel; and what is singular, even when the symptoms had commenced, the application of the cupping-glass had the effect of speedily and completely removing them;—a fact of essential importance in its therapeutical relations.

In these experiments, it would appear, that the poisonous substance was inserted into a wound, and, consequently, immediately into the venous blood, with which it passed on in its circulatory progress. An additional action would, of course, be required to get it through the coats of a sound vessel. In such case, it would have to penetrate by ordinary imbibition; and, having once attained the interior of the vessel, its farther progress would be identical with that of the circulating fluid. Such, then, seem to be the facts regarding the absorbent action of the veins, which rests on as strong evidence as we possess regarding any of the functions of the body. We have yet to inquire into the agents of internal, and adventitious absorptions.

Sect. IV.—INTERNAL ABSORPTION.

On this point but few remarks will be necessary, after the exposition of the different vascular actions, concerned in absorption. This term, comprehends, as we have already remarked,—interstitial absorption, and the absorption of recrementitial, and of excrementitial fluids.—The first comprises the agency, by which the different textures of the body are decomposed and conveyed into the mass of the blood. It will be considered more at length under the head of Nutrition; the second, that of the various fluids, effused into cavities; and the third, that which is effected on the excretions in their reservoirs or excretory ducts.

All these must be effected by one of the two sets of vessels, previously described;—the lymphatics, or veins, or both. We have attempted to show, however, that in all cases an action of selection and elaboration is exerted by lymphatic vessels; whilst we have no evidence of such action in the case of the veins. It would follow, then, that all those varieties of internal absorption, in which the substance, when received into the vessel, possesses different characters from those it had when without, must be executed by lymphatics; whilst those, in which no conversion occurs, take place by the veins. In the constant absorption and corresponding

deposition, which is incessantly going on in the body, the solid parts must be reduced to their elements, and a new compound be formed; inasmuch as we never find bone, muscle, cartilage, membrane, &c. existing in these states in any of the absorbed fluids; and it is probable, therefore, that, at the mouths of the lymphatic vessels, they are all converted into the same fluid—the lymphas the heterogeneous substances, existing in the intestinal canal, afford to the lacteals the elements of a fluid, the character of which is always identical. On the other hand, when the recrementitial fluid consists simply of the serum of the blood, more or less diluted, there can be no obstacle to its passage immediately through the coats of the veins by imbibition, and to its absorption, by the lymphatic vessels also. In the case of the excrementitious fluids, there is reason to believe, that absorption simply removes some of their aqueous portions, and this, it is obvious, can be effected directly by the veins, through imbibition. The facts, connected with the absorption of substances from the interior of the intestine, have clearly shown, that the chyliferous vessels alone absorb chyle; and that the drinks and adventitious substances pass into the mesenteric veins. These apply, however, to external absorption only; but similar experiments and arguments have been brought forward by the supporters of the two opinions, with regard to substances placed on the peritoneal surface of the intestine, and other parts of the body. Whilst some affirm, that they have entered the lymphatics, others have only been able to discover them in the veins. John Hunter, having injected water, coloured with indigo, into the peritoneal cavity of animals, saw the lymphatics, a short time afterwards, filled with a liquid of a blue colour. In animals, which had died of pulmonary or abdominal hæmorrhage, Mascagni found the lymphatics of the lungs and peritoneum filled with blood; and he asserts, that having kept his feet for some hours in water, swelling of the inguinal glands supervened, with transudation of a fluid through the gland, coryza, &c. Desgenettes observed the lymphatics of the liver containing a bitter, and those of the kidneys a urinous, lymph. Soemmering detected bile in the lymphatics of the liver; and milk in those of the axilla. Dupuytren relates a case, which Magendie conceives to be much more favourable to the doctrine of absorption by the lymphatic vessels than any of the others. A female, who had an enormous tumour at the upper and inner part of the thigh, with fluctuation, died at the Hôtel Dieu of Paris, in 1810. A few days before her death, inflammation occurred in the subcutaneous cellular tissue at the inner part of the tuThe day after dissolution, Dupuytren opened the body. On dividing the integuments, he noticed white points on the lips of the incision. Surprised at the appearance, he carefully dissected away some of the skin, and observed the subcutaneous cellular tissue overrun by whitish lines, some of which were as large as a crow's quill. These were evidently lymphatics, filled with puriform mat