ANALYTICAL EVIDENCE. 319 



NOTE (A.) P. 165. 

 ENDOSMOSE AND EXOSMOSE. 



If we place the lower end of an open tube which has 

 been covered with a thin membrane, such as a piece of 

 moistened bladder, in a vessel of water, and pour a solu- 

 tion of sugar into the tube, the water from the vessel will 

 shortly be found to pass into the tube, and the column of 

 liquid will increase in height. At the same time, the 

 water in the vessel will become slightly sweet ; a small 

 quantity of syrup having passed through the pores of the 

 bladder into the water without, while a much larger por- 

 tion of water has entered the tube. The water will con- 

 tinue to enter the tube, and the syrup to leave it, until the 

 two liquids are nearly of the same density. A solution of 

 gum, salt, or other substances may be employed instead 

 of sugar. If two solutions be employed, as, for instance, 

 sugar or gum within the tube, and potash or soda without, 

 a circulation will in like manner take place. Instead of 

 animal membrane, any vegetable matter with fine pores, 

 such as a thin piece of wood, or any porous mineral sub- 

 stance, may be substituted without affecting the result. 

 Dutrochet, the discoverer of these phenomena, gave the 

 name of Endosmose to the inward, and that of Exosmose to 

 the outward movement. He supposed them to be due to 

 two opposite currents of electricity. Dutrochet's hypo- 

 thesis has not been confirmed. It does not constantly 

 happen, that the denser fluid attracts more of the thinner 

 than the latter does of the former ; in the case of gases, 

 especially, the contrary is seen to be sometimes the case. 



