486 ABSORPTION. 



that a limited quantity of liquid can be taken up in this 

 way. 



In view of these facts, it is not necessary to assume the ex- 

 istence of infinitely small capillary openings in homogeneous 

 membranes through which osmotic currents can be made to 

 take place, in order to explain the mechanism of these cur- 

 rents. In the case of two liquids capable of diffusing with 

 each other and separated by an animal membrane, the mech- 

 anism of the endosmotic and exosmotic currents is very 

 simple. In the first place, the membrane imbibes both the 

 liquids, but one is always taken up in greater quantity 

 than the other. If water and a solution of common salt be 

 employed, the surface of the membrane exposed to the water 

 will imbibe more than the surface exposed to the saline solu- 

 tion ; but both liquids will meet in its substance. The first 

 step, therefore, in the production of the currents is imbibi- 

 tion. Once in contact with each other, the liquids diffuse ; 

 the water passing to the saline solution, and vice versa. 

 This takes place by precisely the same mechanism which has 

 been described in connection with the passage of liquids 

 through porous septa. 



In the observations of Porrett, 1 it was observed that the 

 galvanic current was capable of causing water to pass 

 through animal membranes. Carrying out this idea, Dutixv 

 chet first supposed that the attractive force which operated 

 in endosmosis was due to electrical action ; but this view he 

 subsequently abandoned. 2 This theory was afterward ad- 

 vanced by Draper, 3 who noted the fact that a drop of water 

 placed upon the surface of mercury could be made to spread 

 out into a thin film and wet the mercury, by connecting the 

 globule with the positive pole of a galvanic battery and 



1 PORRETT, Curious Galvanic Experiments. Annals of Philosophy, London, 

 1816, vol. viii., p. 74. 



2 Op. cit., p. 70. 



3 DRAPER, On the Mechanical Functions of Areolar Tissues. American Jour 

 nal of the Medical Sciences, August, 1838, p. 308. 



