ENDOSMOSIS. 



105 



and hydrosulphuric acids, added to gum-water, 

 deprived it of the faculty of producing endos- 

 mosis, and that this acidulated water fell in the 

 tube of the endosmometer, instead of rising, as 

 simple gum-water constantly does. The^e facts 

 induced me to say metaphorically that the sul- 

 phuric and hydrosulphuric acids were the ene- 

 mies of endosmosis. 



More recent inquiries have enabled me to 

 see the above mentioned phenomena in ano- 

 ther light. It was the oxalic acid which led 

 me to the conclusions I shall now lay be- 

 fore the reader. Having poured a solution 

 of this acid into the endosmometer closed 

 with a piece of bladder, and placed the re- 

 servoir in water, I found the acid fluid sink 

 rapidly in the tube, and flow towards the 

 inferior water, making its way by filtration 

 through the animal membrane. I then reversed 

 the arrangement observed in this experi- 

 ment. I filled the endosmometer with water, 

 and plunged the reservoir into a solution of 

 oxalic acid. I was now surprised to find the 

 water making its way rapidly into the endos- 

 mometer, and the column rising in the tube, so 

 that, in opposition to all I had yet observed, 

 here was the current of endosmosis directed 

 from the acid towards the water. The follow- 

 ing are the particulars of this experiment. 

 Having poured some rain-water into the reser- 

 voir of the endosmometer, I plunged the reser- 

 voir, closed with a piece of bladder, into a so- 

 lution of oxalic acid of the density of 1.045, 

 (11.6 parts of crystallized acid in 100 of the 

 solution,) the temperature being + 23 cent. 

 The ascent of the water in the tube of the en- 

 dosmometer lasted for three days, becoming 

 gradually slower and slower. The ascent hav- 

 ing then become almost imperceptible, I emp- 

 tied the endosmometer, in the contents of 

 which I found water charged with oxalic acid. 

 The exterior fluid was reduced in density to 

 1.033, so that, whilst the lower acid had pene- 

 trated the upper water by endosmosis, the 

 water had penetrated the acid by exosmosis, 

 and thus diminished its density ; the permea- 

 tion of the water, however, had been less con- 

 siderable than that of the acid ; so that the 

 upper water, increased in volume, had risen in 

 the tube of the endosmometer. We have thus, 

 in the present instance, another obvious proof 

 of the existence of two opposite and unequal 

 currents. Having filled the reservoir of the en- 

 dosmometer anew with rain-water, I placed it in 

 the solution of oxalic acid already used, and of 

 the reduced density of 1.033. The ascent in 

 the tube which again occurred, having almost 

 ceased at the end of two days, I tested the 

 fluid in the endosmometer, and found it to con- 

 tain oxalic acid, and discovered the density of the 

 external fluid further reduced to 1.025. I re- 

 peated the same experiment a third time, filling 

 the reservoir of the endosmometer with rain- 

 water, and plunging it in the old acid solution. 

 Endosmosis went on as before, but with less 

 celerity. Having given up the experiment, after 

 the lapse of twenty-four hours I found the 

 density of the exterior fluid now reduced to 

 1.023, and the internal fluid to contain a por- 



tion of oxalic acid as before. I reduced the 

 densiiy of the exterior acid solution to 1.01, 

 but the included water still gave evidence of a 

 pretty active endosmosis. I reduced the den- 

 sity of the acid to 1.005, (1.2 of acid to 100 

 of the solution,) and the endosmosis was still 

 very remarkable. In these experiments I found 

 that the endosmosis was by so much the more 

 rapid as the exterior acid solution was more 

 dense, so that the capacity of oxalic acid to 

 permeate an animal membrane would appear 

 to increase with the density of its solution in 

 water. In these experiments, too, we observe 

 a fluid, more dense than water, and having a 

 less power of capillary ascent than it, never- 

 theless forming the stronger current, or current 

 of endosmosis, whilst the water opposed to this 

 fluid forms the weaker current, or counter-cur- 

 rent of exosmosis. This is in opposition to all 

 I had observed before ; and the theory I had 

 raised on the different capacities of capillary 

 ascent possessed by two opposed fluids is con- 

 sequently shaken, or at all events proved to be 

 no longer generally applicable. What may be 

 the cause of this new phenomenon ? Do animal 

 membranes give passage more readily through 

 their meshes to solutions of oxalic acid than to 

 water ? This point I sought to determine by 

 the following experiments. 



The filtration of a fluid, by virtue of its gra- 

 vity, through a porous lamina, the capillary 

 canals of which are very minute, is not readily 

 appreciable, unless the inferior or outer surface 

 of this porous plate is kept plunged in or 

 moistened by the same fluid. It is in this way 

 only that the filtration of fluids through animal 

 membranes, the texture of which is dense (a 

 piece of bladder for example,) becomes appre- 

 ciable. It is essential that the inferior aspect 

 of the membrane be bathed with the same fluid 

 as that which rests on its superior aspect, in 

 order that no foreign cause modify its nitration. 

 We know in fact that the heterogeneousness of 

 two fluids, by producing endosmosis, would 

 completely mask the effects of simple filtration. 

 W'ould I, then, try the filtration of water through 

 a membrane, I apply this membrane to an en- 

 dosmometer, which I fill with water to a certain 

 height in the tube of the instrument; I next 

 apply the lower surface of this membrane to 

 the surface of a body of water placed below it. 

 The water contained in the endosmometer filters 

 through the membrane and mingles with the 

 water in the vessel below ; the amount of this 

 filtration in a given time is indicated by the 

 fall of the column in the graduated tube of the 

 instrument. Would I essay comparatively the 

 filtration of any watery solution, I place this 

 solution in the same endosmometer, and taking 

 care to keep the exterior of the membranous 

 part of the instrument in contact with a solution 

 of the same nature, situated below it, I observe 

 the degree to which the depression of the co- 

 lumn in the tube takes place in a space of time 

 equal to that which was taken by the filtration 

 of the water. It is necessary to begin by 

 proving the filtration of water; after this the 

 filtration of the watery solution may be tried ; 

 but it is always to be borne in mind that the 



