332 
PHYSIOLOGY. 
BOOK II. 
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 most pow^erful : and that 
the fluids of plants being more dense than those which sur- 
round them, a similar action takes place between them and 
the water in the soil, by means of which the latter is con- 
tinually impelled into their system. Philosophers do not 
seem disposed to admit the legitimacy of Dutrochet's con- 
clusion, that this transmission takes place by means of galvanic 
agency ; but that the phenomenon is correctly described by 
the ingenious author, and that it is constantly operating in 
plants, is beyond all dispute. It is by endosmose that vapour 
is absorbed from the atmosphere, and water from the earth ; 
that sap is attracted into fruits by virtue of their greater density; 
and probably that buds are enabled to empty the tissue that 
surrounds them when they begin to grow : it will, perhaps, be 
found the most ready explanation of most of the phenomena 
connected with the movement of fluids in plants. 
