330 ENDOSMOSE AND EXOSMOSE. [BOOK n. 



also remarked, that if the experiment was reversed, by filling 

 them with water and immersing them in a denser fluid, the 

 contrary took place, and that the bladders lost weight. He 

 took a small bladder, and filled it with milk, or gum arabic 

 dissolved in water ; to the mouth of this bladder he adapted 

 a tube, and then plunged the bladder in water : in a short 

 time the milk rose in the tube, whence he inferred that water 

 had been attracted through the sides of the bladder. This 

 experiment was also reversed, by filling the bladder with 

 water, and plunging it in milk : the fluid then fell in the 

 tube, whence he inferred that water had been attracted through 

 the coat of the bladder into the milk. From these and other 

 experiments, Dutrochet arrived at the inference, that, if two 

 fluids of unequal density are separated by an animal or vege- 

 table membrane, the denser will attract the less dense through 

 the membrane that divides them : and this property he calls 

 endosmose, when the attraction is from the outside to the 

 inside ; and exosmose, when it operates from the inside to the 

 outside. In pursuing this investigation, he remarked that, if 

 an empty bladder is immersed in water, and the negative pole 

 of a galvanic battery introduced into it, while the positive 

 pole is applied to the water on the outside, a passage of fluid 

 takes place through the membrane, as had previously hap- 

 pened when the bladder contained a fluid denser than water ; 

 by reversing the experiment, the reverse was found to take 

 place : from all which Dutrochet deduces the following 

 theory : That, when two fluids of unequal density are sepa- 

 rated by an intervening membrane, the more dense is nega- 

 tively electrified, and the less dense positively electrified; in 

 consequence of which, two electric currents of unequal power 

 set through the membrane, carrying fluid with them; that 

 which sets from the positive pole, or less dense fluid, to the 

 negative pole, or more dense fluid, being much the more 

 powerful : and that the fluids of plants being more dense than 

 those which surround them, a similar action takes place 

 between them and the water in the soil, by means of which 

 the latter is continually impelled into their system. Philo- 

 sophers do not seem disposed to admit the legitimacy of 

 Dutrochet's conclusion, that this transmission takes place 



