198 ANNUAL OF SCIENTIFIC DISCOVERY. 



is one of the most important to which the attention of the scientific 

 world lias been recently directed, and heralds a great advance in our 

 chemico-physical knowledge. 



To obtain a clear view of the liquid diffusion theory, we must go 

 back more than thirty years, to the period when Dutrochet ex- 

 pounded his important observations on " endosmosis." On the view 

 started by Dutrochet, and founded on his experimental labors, a law 

 was proposed, to the effect that whenever two fluids of different spe- 

 cific gravities, and capable of mixing with each other, are simply sep- 

 arated from each other by a membranous partition, two currents be- 

 come established, one a current proceeding from the outer side of 

 the membrane into the fluid on the inner side ; the other, a current 

 proceeding from the inner side of the membrane to the fluid on the 

 outer side. The first of these processes was called " endosmosis," the 

 second " exosrnosis ; " while, lately, the more general term of "osmo- 

 sis " has been applied to the whole of the phenomena, whether the 

 current set up be mainly from without inwards, or from within out- 

 wards. 



By a variety of experiments, the phenomena of osmosis have been 

 taught and illustrated since the announcement of Dutrochet's origi- 

 nal labors. A gla.'s tube, open at both ends, has been usually em- 

 ployed in the following way. The tube, having had a portion of 

 bladder tied firmly over one of its ends, has been immersed, with the 

 surface of bladder downwards, in a solution of saline or saccharine 

 matter, or into simple water ; the inner part of the tube has then 

 been filled with some saline or saccharine solution, miscible with the 

 solution beneath, but of higher specific gravity. The two solutions 

 left in this manner, with nothing separating them except the septum 

 of organic matter, begin to diffuse ; a portion of the fluid without 

 passes into the cylinder within, through the membrane, while a por- 

 tion of the fluid within passes over to the fluid without, also through 

 the membrane. But whenever the experiment is conducted as we 

 have arranged it, whenever, i. e., the inner fluid is of higher specific 

 gravity than the outer, then the diffusion is much more rapid from 

 without, inwards ; then, consequently, the fluid in the glass cylinder 

 rises above the level of the fluid on the outer side, and then the phe- 

 nomenon of ewc?osmosis is exhibited. If the conditions are reversed, 

 if the denser fluid is placed in the outer cylinder, and the fluid of 

 lower specific gravity in the inner cylinder, then the current set up, 

 being more rapid towards the denser column, the fluid in the outer 

 cylinder rises above the level of the fluid within, and the phenomenon 

 of ezosmosis is exhibited. The transmission of fluids through organic 

 membranes once discovered, the fact soon admitted of demonstration 

 by other methods. For instance, it was shown that the external soft 

 rinds of certain fruits, such as the cherry, could be applied to the pur- 

 pose of illustration ; next it was detected that the animal septum 

 might be replaced by unglazed earthenware ; and on these observa- 

 tions the idea was started, and gained a general acquiescence, that 

 any substance, the pores of which were occupied by water, would sus- 

 tain an uninterrupted liquid communication between two solutions 

 of different densities, and would consequently effect the osmotic pro- 

 cess. 



