28 MOTION OF THE JUICES OF THE ANIMAL BODY. 



through them.* These phenomena may be produced with clay cells ( J ) (such as 

 are used for galvanic apparatus ;) with the lining membrane of the pods of peas 

 and beans ; with the fine inner bark of trees ; with the skin of grapes, of potatoes, 

 of apples ; with the inner membrane of the capsules of bladder senna, &c. ; but 

 animal tissues surpass all others in efficacy. Besides their unequal affinity, they 

 have an unequal absorbent power for dissimilar liquids, by which their action in 

 causing change of volume during mixture is strengthened. 



When a tube, closed with bladder, and filled with water, is immersed in alcohol 

 or brine, there is produced at all points, where the brine or the alcohol comes in 

 contact with bladder saturated with water, a change in the properties of the bladder.! 

 When, in the open pores, the alcohol or brine mixes with the water already there, 

 the absorbent power of the bladder for the water is diminished ; a smaller volume 

 of the mixture is retained than of pure water ; that is to say, water flows out in 

 the direction of the alcohol or brine. This efflux is accompanied by 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 permauent, as long as the liquids do not change in their proper- 

 ties ; but it ceases, in consequence of mixture, and is again restored, when, by mean? 

 of the change of place in both the liquids which are in contact with the opposite sur- 

 faces of the bladder, the original or any other permanent inequality or difference 

 of properties is produced. 



In all cases where a permanent change in the volume of two liquids, separated 

 by a membrane, is observed during their mixture, it is always accompanied 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.'jf. 



From what has been stated, it appears that the change of volume of two miscible 

 liquids, separated by a membrane, is determined by the unequal capacity of being 

 moistened, or the unequal attraction of the membrane for these liquids. The une- 

 qual absorbent power of the membrane for these liquids depends on the dissimilar 

 nature of the liquids or of the substances dissolved in them. An unequal proportion 



(') I consider it of sufficient importance to state here that porous clay also takes up 

 unequal volumes of brine and water. In special experiments made on this subject, 

 cells of clay (moderately ignited porcelain biscuit) were laid for 24 hours in pure water, 

 then carefully dried externally with bibulous paper, and the increase in weight, that is, 

 the weight of the absorbed water, carefully determined.^ The clay was then carefully 

 dried, laid for 24 hours in brine, and the weight of the absorbed brine determined in 

 like manner. In a second series of experiments, the clay cells were steeped in water 

 and brine, and placed in the receiver of the air-pump, under a pressure of 8 lines of 

 mercury (3 of an inch) for 24 hours. 



Under the ordinary pressure, and in air the cells absorbed 



Weight. Volume. 



Water. Brine. Water. Brine 



100 parts of clay cell I. 15'4 14'6 15'4 12'2 



II. 11-8 11-6 11-8 9-7 



In vacuo the cells of clay absorbed 



Weight. Volume. 



Water. Brine. Water. Brine. 



100 parts of clay cell absorbed I. 16-5 16-8 16*5 14*0 



II. 13-8 13-8 13-8 11-5 



* Porous bodies in general exhibit similar phenomena. 



t Bladder shrinks in contact with brine or alcohol. 



J Change of volume in two liquids, separated by membrane, is accompanied by continual 

 tnotion in the particles of the membrane ; and depends on the unequal attraction of the membrane 

 for the liquids. 



$ Amount of liquids absorbed by porous baked clay. 



