310 IMBIBITION AND EXHALATION. 



Generally speaking, endosmosis is more active when the temper- 

 ature is moderately elevated. Dutrochet noticed that an endosmo- 

 meter, containing a solution of gum, absorbed only one volume of 

 water at a temperature of 32 Fahr. ; but absorbed three volumes 

 at a temperature a little above 90. Variations of temperature will 

 sometimes even change the direction of the endosmosis altogether, 

 particularly with dilute solutions of hydrochloric acid. Dutrochet 

 found, for example, 1 that when the endosmometer was filled with 

 dilute hydrochloric acid and placed in distilled water, at the tem- 

 perature of 50 F., endosmosis took place from the acid to the water, 

 if the density of the acid solution were less than 1.020 ; but that it 

 took place from the water to the acid, if its density were greater 

 than this. On the other hand, at the temperature of 72 F., the 

 current was from within outward when the density of the acid solu- 

 tion was below 1.003, and from without inward when it was above 

 that point. 



Finally, the pressure which is exerted upon the fluids and the 

 membrane favors their endosmosis. Fluids that pass slowly under 

 a low pressure will pass more rapidly with a higher one. Different 

 liquids, too, require different degrees of pressure to make them 

 pass the same membrane. Liebig 2 has measured the pressure re- 

 quired for several different liquids, in order to make them pass 

 through the same membrane. He found that this pressure was 



INCHES OF MERCURY. 



For alcohol 52 



For oil . 37 



For solution of salt 20 



For water 13 



There are some cases in which endosmosis takes place without 

 being accompanied by exosmosis. This occurs, for example, when 

 we use water and albumen as the two liquids. For while water 

 readily passes in through the animal membrane, the albumen does 

 not pass out. If an opening be made, for example, in the large 

 end of an egg, so as to expose the shell-membrane, and the whole 

 be then placed in a goblet of water, endosmosis will take place very 

 freely from the water to the albumen, so as to distend the shell- 

 membrane and make it protrude, like a hernia, from the opening in 

 the shell. But the albumen does not pass outward through the 

 membrane, and the water in the goblet remains pure. After a time, 



1 In Milne Edwards, Lemons sur la Physiologie, &c., vol. v. p. 164. 



2 In Longet's Traite de Physiologie, vol. i. p. 384. 



