chap, xxii.] THE OSMOTIC CURRENT. 255 



at the other side. But this liquid, having advanced 

 into the pores, comes into contact with the liquid at 

 the opposite side, and diffusion at once proceeds to 

 take place. The pores thus become occupied by a 

 mixture of two liquids, for one of which it has less 

 affinity than for the other. In consequence of this 

 mixture, then, a new supply of the liquid of greater 

 affinity will advance and displace the mixture, which 

 will flow out on the side of less affinity. As this pro- 

 cess will be constantly repeated, the volume of liquid 

 on the side of less affinity will continually increase. 



This explains the endosmotic current to be due to 

 the unequal affinity of two different liquids for the 

 same membrane. It is, however, unnecessary to sup- 

 pose a similar current in the opposite direction pro- 

 ducing the exosmose. This can be explained, to a 

 great extent, by simple diffusion. For the two 

 liquids are in contact with one another through the 

 pores of the membrane, and consequently diffuse into 

 one another, independently of any aqueous current. 

 Thus the molecules of the salt solution gain access to 

 the water on the other side of the membrane. The 

 diffusion will be aided by the saline solution being in 

 the osmometer, and being, by means of the membrane, 

 kept high in the water, in which it would sink, if 

 free, because of its greater density. The water which 

 has gained the saline side of the membrane, because 

 of its less specific gravity, rises upwards in the 

 saline solution, and this prevents the accumulation of 

 a layer of water next the membrane on the saline side, 

 which, in spite of diffusion, would rapidly interfere 

 with the process ; while whatever of the saline solu- 

 tion has diffused down to the water side of the mem- 

 brane is, by its specific gravity, speedily caused to 

 sink ; and thus is prevented, on the water side, the 

 accumulation of a saline layer, which would interfere 

 seriously with farther progress, 



