Mitchell on the Penetrativeness of Fluids. 115 



A sponge slightly moistened, or dry oat-meal, or any other ab- 

 sorbent, placed by means of a moderate weight closely in contact 

 with the membrane, will, by absorbing the water, cause its continued 

 permeation. 



Even vis a tergo, as in the instance of the gases, will produce 

 infiltration where there exists no other cause of penetration. Over 

 the end of the short limb of an inverted syphon was tied a piece of 

 bladder, and over that, and in close contact with it, was also secured 

 a piece of sheet caoutchouc. Water was then placed in the short 

 limb in communication with the bladder, and thus left for a few 

 hours without compression. No appreciable amount of infiltration 

 ensued. But, in a short time after a column of mercury had been 

 placed in the long limb, water was plainly seen to insinuate itself 

 through the bladder, and to raise up and separate from it the more 

 elastic membrane which surmounted it. After all the water had 

 passed into the space between the two membranes, the syphon was 

 placed in its ordinary position, the end of the long limb resting in 

 the mercury of the trough. Soon the water repassed the bladder, 

 ascended through the short column of mercury lying above it, and 

 collected in the curve which then formed the pinnacle of the appa- 

 ratus. 



Another fact, in itself important, bears forcibly against the electri- 

 cal theory of Dutrochet. To try the absorbent power of the dermoid 

 tissue, pieces of it in a recent state were tied, cuticle outwards, over 

 bottles which contained common air, or carbonic acid gas. Over 

 the bottle which held carbonic acid was inverted a jar of common 

 air, and over that holding air was placed a jar of carbonic acid. The 

 more penetrating gas was, in the first case, in contact with the 

 cuticle, and in the other, with the dissected under surface of the 

 skin. A trial of the contents, after twenty-four hours, showed that 

 much more carbonic acid had penetrated in that apparatus where it 

 was applied to the cuticle, than in the other. As in that case it had 

 gone from the jar into the bottle of common air, while in the other 

 case very little carbonic acid gas had escaped from its receptacle, I 

 filled it again, and tied over it a piece of skin with its cuticle looking 

 inwards. In twenty-four hours the carbonic acid was equally dif- 

 fused through both bottle and jar. Two similar sections of intestine 

 were slightly inflated with common air, one of them being turned in- 

 side out. Both having been carefully tied at the ends, were placed in. 

 identically the same carbonic acid in vessels of equal size. It was 

 soon apparent that the one which had been inverted, filled itself 



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