OSMOSIS. 371 



liquid, or a soluble or minutely -divided solid, may be 

 absorbed by the blood-vessels, provided it is capable of 

 permeating their walls, and of mixing with the blood ; and 

 that of all such substances, the mode and measure of 

 absorption are determined solely by their physical or 

 chemical properties and conditions, and by those of the 

 blood and the walls of the blood-vessels. 



The phenomena are, indeed, exactly comparable to that 

 passage of fluids through membrane, which occurs quite 

 independently of vital conditions, and the earliest and best 

 scientific investigation of which was made by Dutrochet. 

 The instrument which he employed in his experiments was 

 named an endosmometer. It may consist of Fig. 97. 

 a graduated tube expanded into an open- 

 mouthed bell at one end, over which a por- 

 tion of membrane is tied (fig. 97). If now 

 the bell be filled with a solution of a salt 

 say chloride of sodium, and be immersed in 

 water, the water will pass into the solution, 

 and part of the salt will pass out into the 

 water ; the water will pass into the solution 

 much more rapidly than the salt will pass 

 out into the water, and the diluted solution 

 will rise in the tube. To this passage of 

 fluids through membrane the term Osmosis 

 is applied. 



The nature of the membrane used as a 

 septum, and its affinity for the fluids sub- 

 jected to experiment have an important 

 influence, as might be anticipated, on the rapidity and 

 duration of the osmotic current. Thus, if a piece of 

 ordinary bladder be used as the septum between water 

 and alcohol, the current is almost solely from the water to 

 the alcohol, on account of the much greater affinity of water 

 for this kind of membrane ; while, on the other hand, in 

 the case of a membrane of caoutchouc, the alcohol, from 



