108 M. Dutrochet's Discoveries in Vegetable Physiology. 



This effect continues to take place until the difference of pres- 

 sures which the two fluids exert in the ratio of their height is 

 equal to that of the attractions exerted by the two fluids upon 

 the filament of the fluid contained in the capillary pore. 



It follows from this mathematical theory, that there should 

 exist but one single current across the membrane which sepa- 

 rates the two heterogeneous fluids, and that this single current 

 ought to be directed towards that of the two fluids which has 

 the greatest force of attraction. But observation has shown 

 that there exist across the separating membrane two currents, 

 opposite and unequal in force. This fact alone is sufficient to 

 weaken the theory of M. Poisson, and to show that it is to a dif- 

 ferent cause from that which he supposes, that we must attri- 

 bute the phenomenon in question. 



New proofs of this fact are furnished by the following ob- 

 servations. 



If Endosmose and Exosmose are phenomena belonging to 

 capillarity, there ought to exist a constant relation between the 

 height to which different fluids will rise in the capillary tube, 

 and the manner in which they comport themselves in relation 

 to the endosmose and exosmose. 



To make these views more intelligible, let us consider only 

 the phenomenon of the accumulation of fluids which takes 

 place on one of the sides of the separating membrane, and see 

 if this accumulation always takes place on the side where the 

 fluid is, whose ascending power in the capillary tubes is the 

 least considerable, as the theory of M. Poisson supposes, and 

 like that which actually takes place in many circumstances. 



In general the more density a fluid has, the less does it rise 

 in a capillary tube ; but it is not the density here which 

 causes the fluid to ascend less; we know that certain fluids of 

 very small density ascend nevertheless very little in capillary 

 tubes. It is thus that alcohol and ammonia, although less 

 dense than water, ascend much less in capillary tubes than the 

 last fluid. Thus the chemical properties of the fluid produce 

 the same effect as excess of density. But I have remarked, that 

 when pure water is placed in connection, by means of a sepa- 

 rating organized membrane, with a fluid whose ascent in ca- 

 pillary tubes is less than that of the same pure water, we see 



