126 



tremely difficult to conceive how the same air, which 

 is so readily confined in membranous substances out 

 of the body, should, with such perfect freedom, pass 

 to and fro through a much more complicated struc- 

 ture within it. It has indeed been said, that, when 

 any gas is confined in a bladder, it will permeate its 

 coats and escape, while atmospheric air, passing at 

 the same time through these coats, will supply its 

 place. Allowing this to be the case, it will not be 

 denied, that many days, or even weeks, are requi- 

 red to accomplish this operation : and it bears, there- 

 fore, no sort of analogy to that rapid attraction and 

 expulsion of air which is supposed to go on through 

 the cells and blood-vessels of the lungs. It should 

 be remembered also, that the bladder, when remo- 

 ved from the body, soon loses its living properties, 

 by which its power of resisting the passage of fluids 

 may be diminished ; for we know that the bile, a 

 much denser fluid than air, is during life perfectly 

 retained within the gall bladder ; but a short time 

 after death, its colouring matter often escapes, and 

 gives to the surrounding viscera a yellow tinge. 

 Neither can any thing, necessarily residing in the 

 venal blood, be held sufficient to account for this 

 supposed attraction of air ; for Girtanner found, 

 that arterial blood produced the same changes *, and 

 the like occur (97.) when serum only is employed ; 

 and even if, by superior ailinity, the blood did attract 

 air through the coats of the cells and vessels of the 

 Jungs* in what way shall we account for its so ra- 



Mi'ir.oirs on Irritability, p. 228. 23 J. 



