404 
PHYSIOLOGY. 
BOOK II. 
Dutrochet has formed a theory of all the motions of fluids 
in plants depending upon the agency of galvanism. He found 
that small bladders of animal and vegetable membrane, being 
filled with a fluid of greater density than water, securely 
fastened, and then thrown into water, acquired weight; he also 
remarked, that if the experiment was reversed, by filling them 
with water and immersing them in a denser fluid, the con- 
trary took place, and that the bladders lost weight. He took 
a small bladder, and filled it with milk, or gum arabic dis- 
solved 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 experi- 
ment 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 un- 
equal density are separated by an animal or vegetable mem- 
brane, the denser vdll 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 separated by an 
intervening membrane, the more dense is negatively electri- 
fied, 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 sur- 
