MEMBRANE SEPARATING THEM. 55 



the alcohol or brine. This efflux is accompanied 

 bj a change in the volume of the substance of the 

 bladder, for that side of it which is towards the 

 alcohol or the brine contracts or shrinks. 



The opposite surfaces of an animal membrane, in 

 contact with dissimilar liquids, for which they have 

 unequal absorbent power, are in an unequal state of 

 contraction. This condition is permanent, as long 

 as the liquids do not change in their properties ; but 

 it ceases, in consequence of mixture, and is again 

 restored when, by means of the change of place in 

 both the liquids which are in contact with the oppo- 

 site surfaces of the bladder, the original or any 

 other permanent inequality or difference of proper- 

 ties is produced. 



In all cases where a permanent change in the Change of 

 volume of two liquids, separated by a membrane, is 



observed during their mixture, it is always accom- by P mem- 

 panied by a permanent difference in the nature or 

 properties of the two liquids ; and from this it 

 follows, that the molecules of the animal membrane 

 must be, during the mixture, in an alternate state of 

 contraction and swelling, or dilatation ; that is, in a 

 continual motion. 



From what has been stated, it appears that the and de- 

 change of volume of two miscible liquids, separated the un- 

 by a membrane, is determined by the unequal capa- tSon of 

 city of being moistened, or the unequal attraction brane for" 

 of the membrane for these liquids. The unequal 

 absorbent power of the membrane for these liquids 



