Human physiology (Volume 1).

  • Dunglison, Robley, 1798-1869.
Date:
1850
Catalogue details

Licence: Public Domain Mark

Credit: Human physiology (Volume 1). Source: Wellcome Collection.

Provider: This material has been provided by the National Library of Medicine (U.S.), through the Medical Heritage Library. The original may be consulted at the National Library of Medicine (U.S.)

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    It consists of a glass Fig. l. instrument figured in the margin. tube, the lower extremity of which, covered by bladder, is funnel-shaped. ThisM. Dutrochet termed an endosmometer. If an aqueous solution of either gum or sugar be poured into it, and the closed extremity be immersed in pure water, the water is found to pass continually into the tube by filtration through the membrane, so that the liquid will rise in the tube, and may even flow out at the upper aper- ture. At the same time, a portion of the mucilaginous or saccharine solution will escape from the tube through the bladder, and become mixed with the water, but the quan- tity will be much less than that of the water which entered. The facts and arguments adduced by Dr. Mitchell clearly exhibit, that imbibition and transudation are de- pendent upon the penetrativeness of the liquid, and the penetrability of the membrane; that if two liquids, of dif- ferent rates of penetrativeness, be placed on opposite sides of an animal membrane, they will in time present the greater accumulation on the side of the less penetrant liquid, whether more or less dense; but will, finally, tho- roughly, and uniformly mix on both sides; and at length, ^met™0' if any pressure exist on either side, yield to that, and pass to the other side.1 In all such cases, there are both endosmose and exosmose—or double imbibition; in other words, a certain quantity of one fluid passes in, and a certain quantity of the other passes out.2 As a general rule, imbibition takes place from the rarer to the denser medium; from pure water or dilute solutions towards those that are more concentrated. It would appear, again, that the stronger cur- rent is always from the medium which has the strongest affinity for the substance of the septum. It is well known, that in the case of a mix- ture of dilute alcohol covered over by a piece of bladder, the alcohol becomes concentrated, owing to the water—a denser fluid—passing more rapidly through the septum or bladder than the alcohol; but if the same mixture be tied over with elastic gum, the contrary effect will be produced—the alcohol escaping in greater quantity.3 The general conditions of the phenomena of endosmose are:—first, that the two liquids shall have an affinity for the septum or interposed membrane; and, secondly, that they shall have an affinity for, and be miscible with, each other. A portion of the communication of Dr. Mitchell relates to an ana- logous subject, to which, as M. Magendie4 has observed, little or no attention had been paid by physiologists,—the permeability of mem- branes by gases. The laminse, M. Magendie remarks, of which membranes are constituted, are so arranged that gases can penetrate 1 Amer. Journal of the Medical Sciences for November, 1833, p. 100. a Magendie, Lecons sur les Phenomenes Physiques de, la Vie, torn. i. p. 99, Paris, 183G-38. 3 Heule, Allgem. Anat., or Jourdan's French translat., p. 210, Paris, 1843 ; and Wagner, Elements of Physiology, by Willis, p. 438, Loud., 1842. 4 Precis Elementaire de Pliysiologie, 2de edit., 1825, i. 13; and Lecons, &c, torn. i. p. 132.