ABSORPTION OF T11E DIGESTIVE CAVITY. 195 



into that liquid, giving rise to the appearance of a fluid current in the 

 opposite direction. The great importance of the nature of the septum and 

 of its capacity for imbibing or for being permeated by the liquids, is shown 

 by the facility with which the experiment can be arranged in such a manner 

 that a current shall only pass in one direction ; for if the mouth of the instru- 

 ment be closed with bladder, and alcohol be placed within it, on immersing 

 it in water a current is immediately established from the water to the alcohol, 

 the increased bulk of which can be ascertained by a scale attached to the 

 upper part of B, but there will be no evidence of a counter current passing 

 from the alcohol to the water. If on the contrary, the mouth of the instru- 

 ment be closed with a thin lamina of caoutchouc, a current soon sets from 

 the alcohol to the water, and therefore in the opposite direction. We may 

 explain these phenomena by supposing that in the former instance the water 

 possesses a superior attraction for the membrane, enters its pores by imbibition 

 and capillary attraction, and driving the alcohol- before it, reaches the inner 

 surface of the membrane, whence it instantly diffuses into that fluid, partly 

 in consequence of the mutual repulsive force of its own particles, and partly 

 from their affinity to those of the alcohol. In the latter case the alcohol 

 exerts the same influence by virtue of its superior affinity for the caoutchouc. 

 Professor Graham, indeed, considers that the water movement in osmosis is 

 simply an affair of hyd ration and dehydration of the substance of the mem- 

 brane or other colloid septum, and that the diffusion of the saline solution 

 placed within the osmometer has little or nothing to do with the osmotic re- 

 sult otherwise than as it affects the state of hydration of the septum. 1 



139. It is not absolutely necessary that the septum should be of a solid 

 nature, since the same phenomena are observed where, as in L'Hermite's 

 experiment, 2 a layer of water constitutes the diaphragm, being made to 

 separate a subjacent and heavier layer of chloroform from a superjaceut and 

 lighter layer of ether. The water is impermeable to chloroform, but perme- 

 able to ether, which, therefore, gradually penetrates through the water to 

 the chloroform, and from its affinity for the latter, immediately diffuses 

 into it, ultimately, in opposition to the force of gravity, entirely disappear- 

 ing from the surface of the water. The importance of the miscibility of the 

 fluids is clearly shown by the complete absence of currents which occurs 

 when the fluids on the opposite sides of the septum have no affinity for one 

 another, as in the case of oil and water, or of water and chloroform. But 

 even when such affinity really exists, and when, as is usually the case in the 

 animal body, there is more or less tendency in the fluids on the opposite 

 sides of the septum to diffuse into one another, many circumstances may in- 

 terfere to modify the force and direction of the osmotic currents besides those 

 already noticed. Amongst these may be mentioned temperature, 3 pressure, 

 electricity, 4 the specific heat of the fluids, 5 the process of evaporation, the 

 previous impregnation of the membrane with acids, 6 or alkalies, 7 and lastly, 

 one which is in constant operation in the living body, viz., the movement 

 of one of the fluids, the effects of which may be clearly exhibited by means 

 of an apparatus essentially the same as that constructed by Dr. Robinson, 

 and shown in Fig. 82, where B is a vessel containing colored fluid ; c a piece 

 of intestine attached to the stopcock of B on the one hand, and to a siphon 

 on the other, and immersed in a vessel of water, A. If the siphon be of 



1 For a theory which is in close accordance with this, see Buchheimer (Beitrage) 

 Archiv f. Phys. Heilk., 1853, t. xii. 



2 Comptes Rendus, 1855, p. 1179. ' Eckhard, Beitrage, 1858, p. 9"). 



4 Brooke, Nat. Phil., 18GO. 5 BSulard, Physiologic, 1802, p. 170. 



6 Harzor, Archiv f Phys. Hoilk., 1850, t. xv. 



7 Wistinghausen, Dissert., Dorpat, 1851. 



