ABSORITION". 409 



in his experiments was named an endosmometer. One form of this, 

 represented in the figure, consists of a graduated tuhe expanded into an 

 open-mouthed bell at one end, over which a portion of memhrane is 

 tied. If the bell be filled with a solution of a salt say sodium chloride, 

 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, however, will 

 pass into the solution much more rapidly than the salt will pass out into 

 the water, and the dilated solution will rise in the tube. It is to this 

 passage of fluids through membrane that the term osmosis is applied. 

 The nature of the membrane used as a septum, and its affinity for 

 the fluids subjected to experiment have an important influ- 

 ence, as might be anticipated, on the rapidity and dura- 

 tion 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 its greater 

 affinity for this substance, would pass freely into the water. 

 Absorption by blood-vessels is the consequence of their 

 walls being, like the membranous septum of the endosmo- 

 meter, porous and capable of imbibing fluids, and of the 

 blood being so composed that most fluids will mingle with 

 it. Thus the relation of the chyme in the stomach and 

 intestines to the blood circulating in the vessels of the 

 gastric and intestinal mucous membrane is evidently just 

 that which is required for osmosis. The chyme contains 

 Fig. 275 substances which have been so acted upon by the di- 



Endosmometer. 



gestive juices as to have become quite able to pass through 

 an animal membrane, or to dialyze as it is called. The thin animal 

 membrane is the coat of the blood-vessels with the intervening mucous 

 membrane. The nature of the fluid within the vessels, the very feeble 

 power of dialyzation which the albuminous blood possesses, determines 

 the direction of the osmotic current, viz., into and not out of the blood- 

 vessels. The current is of course aided by the fact of the constant 

 change in the blood presented to the osmotic surface, as it rapidly circu- 

 lates within the vessels. As a rule the current is from the stomach or 

 intestine into the blood, but the reversed action may occur, when, for 

 example, sulphate of magnesia is taKen into the stomach, in which case 

 there is a rapid discharge of water from the blood-vessels into the ali- 

 mentary canal resulting in purgation. The presence of various sub- 

 stances in the food has the power of diminishing the rate of absorption; 

 their influence is probably exerted upon the membrane, diminishing its 

 power of permitting osmosis. Whereas the presence of a little hydro- 



