500 ABSORPTION. 



through an animal membrane with pure water on either side, 

 by simply immersing in the fluids the poles of a galvanic 

 battery, 1 and the experiments of Dutrochet, who produced 

 currents in the same way through the caecum of the fowl, 2 

 the idea was advanced that all endosmosis was dependent 

 upon galvanic action. !N"o one, however, has ever professed 

 to have detected a galvanic current during ordinary endos- 

 mosis, by the galvanometers usually employed, and this the- 

 ory is without any positive basis. 



These observations of Porrett and Dutrochet have been 

 repeatedly verified by later experimenters. They showed a 

 tendency to diffusion in two portions of the same liquid, 

 separated by a membrane, when one was charged with posi- 

 tive and the other with negative electricity, the current tak- 

 ing place from the positive to the negative pole. Under 

 these circumstances, the endosmotic current is actually pro- 

 duced by galvanic action, for it never takes place when the 

 liquids on either side of the membrane are identical. Other 

 experiments, which it is unnecessary to refer to in detail, 

 have shown that the phenomena of osmosis between liquids 

 of different constitution may be modified by galvanic action, 

 that the currents may be established in this way where they 

 would not otherwise take place, and that existing currents 

 may be arrested or even reversed. The experiments of 

 Fodera (which were made upon living animals before the 

 description of endosmosis by Dutrochet), are striking exam- 

 ples of the influence of electricity upon the passage of solu- 

 tions through animal membranes. This observer found that 

 while it required from half an hour to an hour and a half for 

 a solution of sulphate of iron and a solution of prussiate of pot- 

 ash, placed upon either side of an animal membrane, to pene- 

 trate its substance and produce the characteristic blue reac- 

 tion, when the liquids were connected with the poles of a gal- 



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

 1816, vol. viii., p. 74. 



2 Op. tit, p. 71. 



