PHYSICAL PROPERTIES OF TISSUES. 



67 



instrument figured in the margin. It consists of a glass 

 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, 

 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. Magendie 4 has observed, little or no 

 attention had been paid by physiologists, the permeability of mem- 

 branes by gases. " The laminae," 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. 

 3 Magendie, Le$ons sur les Phenomenes Physiques de la Vie, torn. i. p. 99, Paris, 

 1836-38. 



3 Henle, Allgem. Anat., or Jourdan's French translat., p. 210, Paris, 1843; and Wagner, 

 Elements of Physiology, by Willis, p. 438, Lond., 1842. 



4 Precis Elementaire de Physiologie, 2de edit., 1825, i. 13; and Leeons, &c., torn. i. p. 

 132. 



