] 16 Mitchell on the Penetrativeness of Fluids. 



most rapidly, and although rather less than the other, soon greatly 

 exceeded it in size and hardness. After remaining so exposed for 

 eighteen hours, vessels of common air were placed over the dis- 

 tended bags, when a diminution of volume became in time apparent, 

 and was more rapid considerably in the specimen which had not 

 been inverted. It appears, then, that the transmission of a gas is 

 easiest where it is placed on the cuticular or mucous surface of an 

 animal membrane, rather than on its cellular or peritoneal surface, 

 a fact to be kept in view in rating the transmissibility of the dif- 

 ferent gases or liquids. The fluids should be compared under ex- 

 actly similar circumstances, standing in the same relation to the 

 surfaces of the membrane used. 



In the following experiment, made with great precaution, we per- 

 ceive a result distinctly indicative of the superior penetrability of the 

 cuticular surface. Over the mouths of two phials, accurately filled 

 with alcohol, weighing, according to a Pese-Ether, thirty-five and 

 a quarter, were tied two pieces of human skin. In one the raw side 

 presented, in the other the cuticular side. Both were placed mouth 

 downwards in similar specimens of water, with columns of equal 

 altitude. After the lapse of twenty-four hours, the alcohol was exa- 

 mined, and found to weigh more, by at least one degree, in the 

 phial which presented the cuticle to the water. In it the ethero- 

 meter sunk to thirty-three and a half, while in that which presented 

 the dissected surface to the water it fell only to thirty-four and a 

 half. The one had been reduced by the water one degree and three- 

 fourths, and the other only three-fourths of a degree. 



In all these cutaneous experiments, we perceive not only the 

 agency of the membrane itself, but even that of its respective sur- 

 faces, so that we are not at liberty to admit the assertion respecting 

 the action of the liquids, as independent of the influence of the inter- 

 vening membrane. 



In truth, it is now manifest that the liquid, if penetrative, per- 

 meates a given tissue at a rate dependent on the character of tissue 

 and power of penetration. If on the opposite side there exist a sub- 

 stance or power capable of occupying or removing it as fast as, or 

 faster than the membrane delivers it, the actual rate of transmission 

 will be as high as is possible ; but if not so capable, the accumulation 

 will be at a lesser rate, and will represent the degree of permeability 

 of the inviting substance alone. Thus, for illustration, if ether can 

 convey away water as fast as, or faster, than the membrane can 

 transmit it, the rate of penetration will be the greatest possible, and 



