DO MATERIAL COMPOSITION OF MAN. 



Togno, 1 of Philadelphia; and with like results. The fact of this imbi- 

 bition and transudation was singular and impressive; and, with so 

 enthusiastic an individual as M. Dutrochet, could not fail to give birth 

 to numerous and novel conceptions. The energy of the action of both 

 endosmose and exosmose is in proportion, he asserted, to the difference 

 between the specific gravities of the two fluids; and, independently of 

 their gravity, their chemical nature affects their power of transmission. 

 These effects he at once decided must be owing to electricity. The 

 cavities, in which the changes take place, he conceived to be like Ley- 

 den jars having their two surfaces charged with opposite electricities, 

 the ultimate effect or direction of the current being determined by the 

 excess of the one over the other. 



In an inferesting and valuable communication by Dr. J. K. Mitchell, 2 

 of Philadelphia, "on the penetrativeness of fluids," many of the vision- 

 ary speculations of M. Dutrochet are sensibly animadverted upon. 

 It is there shown, that he had asserted, in the teeth of some of his 

 most striking facts, that the current was from a less dense to a more 

 dense fluid; and that it was from positive to negative, dependent not 

 on an inherent power of filtration, a power always the same when the 

 same membrane is concerned, but modified at pleasure by supposed 

 electrical agencies. This view was subsequently abandoned by M. 

 Dutrochet, in favour of the following principle. It is well known that 

 porous bodies, as sugar, wood, or sponge, are capable of imbibing 

 liquids, with which they are in contact. In such case the liquid is not 

 merely introduced into the pores of the solid, as it would be into an 

 empty space; but is forcibly absorbed, so that it will rise to a height 

 considerably above its former level. This force is molecular, and is 

 the same that we witness in the phenomena presented by the capillary 

 tube, which affords us the simplest case of the insinuation of a liquid 

 into a porous body. It cannot alone, however, cause the liquid to pass 

 entirely through the body. If a capillary tube, capable of raising 

 water to the height of six inches, be depressed, so that one inch only 

 be above the surface, the water will rise to the top of the tube; but no 

 part of it will escape. Even if the tube be inserted horizontally into 

 the side of the vessel containing water, the water will only pass to the 

 end of the tube. The same thing occurs when a liquid is placed in 

 contact with one side of a porous membrane: it enters the pores; passes 

 to the opposite side, and is there arrested. But if this membrane com- 

 municates with a second vessel containing a different liquid as a saline 

 solution, capable of mixing with the first, and affected to a different 

 degree by capillary attraction a new phenomenon will be presented. 

 It will be found, that both liquids enter the pores, and pass through to 

 the opposite side. They will not, however, be carriqd through with the 

 same force: that which has the greatest power of capillary ascension, 

 has the greatest affinity for the membrane, or will wet it more readily, 

 in other words, that which will rise the highest in a capillary tube, 

 will pass through in greater quantity, and cause an accumulation of 

 liquid on the opposite side. The action is well shown by the simple 



1 Amer. Journal of the Med. Sciences, iv. 73, Philad., 1829. 

 9 Ibid., vii. 23, Philad., 1830. 



