IV. INTERNAL ABSORPTION. On this point but few remarks will be necessary, after the exposition of the different vascular actions concerned in absorption. The term comprehends interstitial absorption, and the absorption of recrementitial fluids. The first comprises the agency by which the different textures of the body are decomposed and conveyed into the mass of 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 accomplished by one of the two sets of vessels previously described; lymphatics, or veins, or both. Now, we have attempted to show, that an action of selection and elaboration is exerted by lymphatics; whilst we have no evidence of such action in the case of the veins. It would follow, then, that all the 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, 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 radicles of the lymphatic vessels, they are converted into the same fluid-the lymph-in like manner as the heterogeneous substances 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 the passage of its aqueous portion immediately through the coats of the veins by imbibition, whilst the more solid part is taken up by the lymphatic vessels. In the case of 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, in 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. Mr. 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, that had died of pulmonary or abdominal hemorrhage, 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. M. Desgenettes observed the lymphatics of the liver containing a bitter, and those of the kidneys a urinous, lymph. Sömmering detected bile in the lymphatics of the liver; and milk in those of the axilla. M. Dupuytren relates a case, which M. 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 fluctuating tumour at the upper and inner part of the thigh, died at the Hôtel Dieu, of Paris, in 1810. A few days before her death, inflammation occurred in the subcutaneous areolar tissue at the inner part of the tumour. The day after dissolution, M. 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 areolar tissue overrun by whitish lines, some of which were as large as a crow's quill. These were evidently lymphatics filled with puriform matter. The glands of the groin, with which these lymphatics communicated, were injected with the same matter. The lymphatics were full of the fluid, as far as the lumbar glands; but neither the glands nor the thoracic duct presented any trace of it. On the other hand, multiplied experiments have been instituted, by throwing coloured and odorous substances into the great cavities of the body; and these have been found always in the veins, and never in the lymphatics. To the experiments of Mr. Hunter, objections have been urged, similar to those brought against his experiments to prove the absorption of milk by the lacteals; and sources of fallacy have been pointed out. The blue colour, which the lymphatics seemed to him to possess, and which was ascribed to the absorption of indigo, was noticed in the experiments of Messrs. Harlan, Lawrence, and Coates; but they discovered that this was an optical illusion. What they saw was the faint blue, which transparent substances assume, when placed over dark cavities. Mr. Mayo has also affirmed that the chyliferous lymphatics always assume a bluish tint a short time after death, even when the animal has not taken indigo. The cases of purulent matter, &c., found in the lymphatics, may be accounted for by the morbid action having produced disorganization of the vessel, so that the fluid could enter the lymphatics directly; and, if once within, its progression could be readily understood. M. Magendie asserts, that M. Dupuytren and he performed more than one hundred and fifty experiments, in which they submitted to the absorbent action of serous membranes different fluids, and never found any of them within the lymphatic vessels. These fluids produced their effects more promptly, in proportion to the rapidity with which they were capable of being absorbed. Opium exerted its narcotic influence; wine produced intoxication, &c., and M. Magendie found, from numerous experiments, that the ligature of the thoracic duct in no respect diminished the promptitude with which these effects supervened. The 1 Magendie, Précis, &c., 2de édit., ii. 195, et seq.; and Adelon, art. Absorption, Dict. de Méd., 2de édit., i. 239, and Physiologie de l'Homme, 2de édit., iii. 65, Paris, 1829. 2 Harlan's Physical Researches, p. 459, Philad., 1835. 4 Op. cit., ii. 211. partisans of lymphatic absorption, however, affirm that even if these substances are met with in the veins, it by no means follows, that absorption has been effected by them; for the lymphatics, they assert, have frequent communications with the veins; and, consequently, they may still absorb and convey their products into the venous system. In reply to this, it may be urged, that all the vessels-arterial, venous, and lymphatic-appear to have intercommunication; but there is no reason to believe, that the distinct offices, performed by them, are, under ordinary circumstances, interfered with; and, again, where would be the necessity for these intermediate lymphatic vessels, seeing that imbibition is so readily effected by the veins? The axiom-quod fieri potest per pauca, non debet fieri per multa—is here strikingly appropriate. The lymphatics, too, as we have endeavoured to show, exert an action of selection and elaboration on substances exposed to them; but, in the case of venous absorption, there is not the slightest evidence, that any such selection exists,-odorous and coloured substances retaining, within the vessel, the properties they had without. Lastly. Where would be the use of organs of a distinct lymphatic circulation opening into the thoracic duct, seeing that the absorbed matters might enter the various venous trunks directly through these supposititious communicating lymphatics; and ought we not occasionally to be able to detect in the lymphatic trunks some evidence of those substances, which their fellows are supposed to take up and convey into the veins? These carrier lymphatics have obviously been devised to support the tottering fabric of exclusive lymphatic absorption,-undermined, as it has been, by the powerful facts and reasonings that have been adduced in favour of absorption by veins. From the whole of the preceding history of absorption, we are of opinion, that the chyliferous and lymphatic vessels form only chyle and lymph, refusing all other substances, with the exception of saline and other matters, that enter probably by imbibition,-that the veins admit every liquid, which possesses the necessary tenuity; and that whilst all the absorptions, which require the substances acted upon to be decomposed and transformed, are effected by chyliferous and lymphatic vessels; they that are sufficiently thin, and demand no alteration, are accomplished directly through the coats of the veins by imbibition; and we shall see that such is the case with several of the transudations or exhalations. V. ACCIDENTAL ABSORPTION. The experiments, to which reference has been made, have shown, that many substances, adventitiously introduced into various cavities, or placed in contact with different tissues, have been rapidly absorbed into the blood, without experiencing any transformation. Within certain limits, the external envelope of the body admits of this function; out by no means to the same extent as its prolongation, which lines the different excretory ducts. The absorption of drinks is sufficient evidence of the activity of the function as regards the gastro-enteric mucous membrane. The same may be said of the pulmonary mucous membrane. Through it, oxygen and nitrogen pass to reach the blood in the lungs, as 1 well as carbonic acid in its way outwards. Aromatic substances, such as spirit of turpentine, breathed for a time, are detected in the urine; proving that their aroma has been absorbed; and it is by absorption, that contagious miasmata probably produce their pestiferous agency. Dr. Madden, however, thinks that the lungs do not absorb watery vapour with the rapidity, or to the extent, that has been imagined; whilst Dr. A. Combe' hazards the hypothesis, that owing apparently to the extensive absorption of aqueous vapour by the lungs, the inhabitants of marshy and humid districts, as the Dutch, are remarkable for the predominance of the lymphatic system. Not only do the tissues, as we have seen, suffer imbibition by fluids, but by gases also: the experiments of Chaussier and Mitchell astonish us by the rapidity and singularity of the passage of the latter through the various tissues;-the rapidity varying according to the permeability of the tissue, and the penetrative power of the gas. 5 6 a. Cutaneous Absorption. 8 On the subject of cutaneous absorption, much difference of sentiment has prevailed; some asserting it to be possible to such an extent, that life may be preserved, for a time, by nourishing baths. It has also been repeatedly affirmed, that rain has calmed the thirst of shipwrecked mariners who have been, for some time, deprived of water. It is obvious, from what we know of absorption, that, in the first of these cases, the water only could be absorbed; and even the possibility of this has been denied by many. Under ordinary circumstances, it can happen to a trifling extent only, if at all; but, in extraordinary cases, where the system has been long devoid of its usual supplies of moisture, and where we have reason to believe, that the energy of absorption is increased, such imbibition may be possible. Sanctorius,3 Von Gorter,* Keill, Mascagni, Madden," R. L. Young, Dill, and others believe, that this kind of absorption is not only frequent but easy. It has been affirmed, that after bathing the weight of the body has been manifestly augmented; and the last of these individuals has adduced many facts and arguments to support the position. Strong testimony has been brought forward in favour of extensive absorption of moisture from the atmosphere. This is probably effected rather through the pulmonary mucous surface than the skin. A case of ovarian dropsy is referred to by Dr. Madden,10 in which the patient, during eighteen days, drank 692 ounces of fluid; and discharged by urine and paracentesis 1298 ounces, being an excess of 606 ounces of fluid egesta over the fluid ingesta. Bishop Watson, in his Chemical Essays, states, that a lad at Newmarket, having been almost starved, in order that he might be reduced to the proper weight for riding a match, was weighed at 9, and again at 10, A. M., when he was found to have gained nearly 30 1 Experimental Inquiry into the Physiology of Cutaneous Absorption, p. 64, Edinb., 1838. 2 Principles of Physiology applied to the Preservation of Health, 5th edit, p. 72, Edinb., 1836. 3 De Static. Medic., Lugd. Bat., 1711. 5 Tentamin. Medico-Physic., Lond., 1718. 7 Op. cit., p. 58. 9 Edinb. Medico-Chir. Transact., ii. 350. 4 De Perspirat. Insensib., Lugd. Bat., 1736. 6 Vas. Lymphat. Hist., Senis, 1783. ounces in weight in the interval, although he had only taken half a glass of wine. Dr. Carpenter' gives a parallel case, which was related to him by Sir G. Hill, Governor of St. Vincent. A jockey had been for some time in training for a race in which Sir G. Hill was much interested, and had been reduced to the proper weight. On the morning of the race, suffering much from thirst, he took one cup of tea, and shortly afterwards his weight was found to have increased six pounds, so that he was incapacitated for riding. These cases certainly appear difficult of belief: yet the authority is good. Dr. Carpenter presumes, that nearly the whole of the increase in Bishop Watson's case, and at least three fourths of it in Sir G. Hill's case, must be attributed to cutaneous absorption, which was probably stimulated by the wine that was taken in the one, and by the tea in the other. Bichat was under the impression, that, in this way he imbibed the tainted air of the dissecting room, in which he passed a large portion of his time. To avoid an objection, that might be urged against this idea,-that the miasmata might have been absorbed by the air passages, he so contrived his experiment, as, by means of a long tube, to breathe the fresh outer air; when he found, that the evidence, which consisted in the alvine evacuations having the smell of the miasmata of the dissecting-room, continued. It is obvious, however, that such an experiment would hardly admit of satisfactory execution, and it is even doubtful, whether there was any actual relation between the assigned effect and the cause. The testimony of MM. Andral, Boyer, Duméril, Dupuytren, Serres, Lallemand, Ribes, Lawrence, Parent-Duchatelet, and that afforded by the author's own observation, are by no means favourable to the great unwholesomeness of cadaveric exhalations.2 Dr. J. Bradner Stuart3 found, after bathing in infusions of madder, rhubarb, and turmeric, that the urine was tinged with these substances. A garlic plaster affected the breath, when every care was taken, by breathing through a tube connected with the exterior of the apartment, that the odour should not be received into the lungs. Dr. Thomas Sewall found the urine coloured, after bathing the feet in infusion of madder, and the hands in infusions of madder and rhubarb. Dr. Mussey' proved, that if the body be immersed in a decoction of madder, the substance may be detected in the urine, by using an appropriate test. Dr. Barton found, that frogs, confined in dry glass vessels, became enfeebled, diminished in size, and unable to leap; but that, on the introduction of a small quantity of water, they soon acquired their wonted vigour, became plump, and as lively as usual in their motions. M. W. F. Edwards of Paris, is, also, in favour of absorption being carried on by the skin to a considerable extent. 1 Human Physiology, § 462, Lond., 1842. 2 Parent-Duchatelet, Hygiène Publique, Paris, 1836; and the remarks of the author in his Human Health, p. 77, Philad., 1844. 3 New York Med. Repos., vols. i. and iii. 1810-11. 4 Med. and Physical Journ., xxxi. 80, Lond., 1814. 5 Philad. Medical and Physical Journal, i. 288, Philad., 1808. 6 Klapp, Inaugural Essay on Cuticular Absorption, p. 30, Philad., 1805. 7 Sur l'Influence des Agens Physiques; or Drs. Hodgkin and Fisher's translation, p. 61, and p. 187, &c., Lond., 1832. |