Mitchell on the Penetrativeness of Fluids. 113 



so much more rapidly than ether or alcohol as to swell the amount 

 of liquid on their side. 



When alcohol is largely diluted with water it penetrates an ani- 

 mal membrane more easily itself, and offers to the pure water which 

 reaches it from the opposite side less invitation to infiltrate it, ac- 

 cording to a law of progressive diminution, pointed out by our expe- 

 riments on gases. Such a diluted portion of alcohol placed by M. 

 Dutrochet in his endosmometer, and raised above the level of the 

 pure water on its outside, found, in the force of the higher column, 

 sufficient cause for its escape, which continued until the level was 

 reached, when action apparently ceased. If the level be obtained 

 at the commencement of the experiment, either no appreciable 

 change is observed, or the movement is unquestionably in a direc- 

 tion contrary to that stated by Dutrochet. So, when gases are 

 permeating in opposite directions any interposed membrane, the 

 penetration soon begins to lessen, because there is on either side 

 less porosity unoccupied, and there is also in them the repellent 

 character of their gaseous state. M. Dutrochet reconciles these 

 apparently contradictory facts to his system, by supposing chemical 

 influence to produce the first, and electricity the second. In either 

 case, he does not appear to dream of independent and original pow- 

 ers of penetration, by which the liquid comes through to the opposite 

 side of the membrane, remaining in its tissue, or passing on by a 

 similar power of infiltration into new matter, or, such matter being 

 absent, accumulating on that side by the influence of mechanical 

 power, or electrical excitement, or chemical combination, truths 

 adequately demonstrated by my experiments on gases. 



The blinding effect of preconception on the most philosophic and 

 candid mind can perhaps have no better exemplification than is 

 afforded by what M. Dutrochet says relative to the point of accumu- 

 lation, when a diluted acid and water were placed on opposite sides 

 of an animal membrane. As alkalies produced towards them a cur- 

 rent for the support of his electrical theory, acids should be found to 

 set the current towards water, and he found it so. In my experi- 

 ments, the greater current was always towards the acid, and not 

 from it ; and I find that Dr. WEDEMEYER (Untersuchungen iiber 

 der Kreislauf des Bluts, &c.) has made the experiment with a like 

 result. On reference to Dr. TOG NO'S experiments (Amer. Journ. of 

 Med. Sci.), which were chiefly repetitions of those of Dutrochet, we 

 perceive that he does not seem to be satisfied perfectly with the 

 report of Dutrochet on this subject. Let any one desirous of testing 

 this matter, tie a piece of animal membrane over the end of a hollow 

 Voi II. AUG. 1831. I 



