252 PHYSIOLOGICAL PHYSICS. [Chap. xxn. 



a saline solution, its lower end is plunged into dis- 

 tilled water, in a very short time the liquid rises 

 in the tube, and some of the salt may be detected in 

 the surrounding water. It appears as if a current 

 had been set up from water through the membrane to 

 the saline solution, and a second current from saline 

 solution to water through the membrane, the former 

 being greater, and consequently raising the level of 

 the fluid in the tube. To the first current Dutrochet 

 applied the term ENDOSMOSIS, to the second, EXOSMOSIS. 



The question of two contrary currents will be 

 considered immediately ; first of all, however, the 

 facts of the interchange must be stated with a little 

 more detail. Dutrochet's early experiment is thus 

 described : "I took the cseca of young chickens : I 

 filled them with liquids more dense than water, such 

 as milk, a solution of gum, of the albumen of egg, etc., 

 and after having closed them by a ligature I plunged 

 them into water. The intestines speedily became 

 swollen up and turgid by the introduction of water 

 into their interior ; their weight increased consider- 

 ably."* The general fact is, that if two dissimilar 

 liquids are separated by an animal membrane, mixture 

 can go on through the membrane. A porous diaphragm 

 may take the place of the membrane without inter- 

 fering with the process. 



The instrument employed by Dutrochet for his 

 later experiments, and that usually employed, consists 

 of a glass tube R?/, having at one end a bell-jar-shaped 

 expansion J. The mouth of the jar is tightly closed, 

 usually with thin animal membrane m. Down the tube 

 is poured the saline or other solution, and the instru- 

 ment, termed an OSMOMETER (Fig. 116), is immersed 

 in a jar F containing distilled water, the water out- 

 side standing to a level x with the solution inside. 



* Dutrochet, "Memoires pour servir a 1'histoire anatomique et 

 physiologique des vegetaux et desanimaux," p. 8. Paris, 1837. 



