DIALYSIS. 613 



a current of itself), and osmosis will cease. If these portions be 

 moved away, however, before or as soon as the equal density is at- 

 tained, and their place supplied by fresh portions, the current will be 

 continued. 



8. Decomposition of the animal membrane produces a cessation of 

 the current. 



4. Certain substances of animal and vegetable origin are said to in- 

 terfere with osmosis, as morphia, the woorara poison, the rabies of 

 dogs, the poison of small-pox. The last three substances have been 

 taken into the stomach without harm, while morphia is said to prevent 

 osmosis of the fluids of the blood when introduced into the circulation. 



5. It has already been stated that pressure exerts an important 

 influence upon osmosis. It is under the influence of pressure that al- 

 bumen, which does not ordinarily osmose, is caused to pass through 

 animal membrane in certain pathological states, as where albumen 

 passes through the bloodvessels into the uriniferous tubules of the 

 kidney and appears in the urine. 



Little further need be said of osmosis in connection with the func- 

 tions of the body in which it plays a part, save for purposes of illus- 

 tration. In the operation of absorption, it is of course very largely 

 concerned; a glass of water taken into the stomach rapidly disap- 

 pears, being absorbed by the endosmotic agency of the bloodvessels. 

 Here is plainly seen the primary importance of change of place or 

 motion on the part of at least one of the fluids separated by the mem- 

 brane. Were this not the case, an equilibrium would soon be ob- 

 tained and the current be discontinued ; but the rapidity of the circu- 

 lation in the capillaries carries away the water absorbed, and leaves 

 room for the absorption of more. 



On the same principle, fulness of the capillaries retards osmosis; 

 whence an important practical deduction follows with regard to the 

 treatment of poisoned wounds. If by any means at our disposal we 

 can bring about a congestion of the bloodvessels surrounding the 

 wound, the tendency to absorption of the poison will be greatly dimin- 

 ished. And this is the principle upon which the application of a cup- 

 ping-glass to the wound, as revived by Sir D. Barry, or a ligature 

 placed between tbe wound and the central organ of circulation, or even 

 suction applied to the wound itself, will sometimes prevent the action 

 of the poison. 



The experiments of Christison and Magendie are illustrations of 

 these facts. The former, after tying a ligature about the limb of 

 a dog, introduced some poisonous material into the connective tissue 

 beyond the ligature. So long as the ligature was allowed to remain, 

 very little absorption took place ; but immediately on the removal of 

 the ligature and the renewal of circulation, the animal succumbed.* 

 Magendie injected a colored liquid into the cavity of the peritoneum 

 of an animal, having first also produced a plethoric condition of the 

 bloodvessels by injecting them with water. So long as the plethoric 



* Christison on Poisons, p. 39. 



