chap, xxii.] PHYSICS OF ABSORPTION. 263 



with any current from the blood outwards into the 

 cavity of the stomach, and so will act in the same 

 direction as the serum of the blood, in determining 

 the current from the stomach inwards to the 

 capillaries. Besides all this, in the case of the 

 stomach and intestinal canal are to be found all the 

 other conditions favouring the passage of fluid con- 

 taining substances in solution from the cavity of the 

 alimentary canal to the current of the circulation. 

 Thus it has been pointed out that, if the fluid on each 

 side of the membrane were stationary, the inter- 

 changes would speedily become feeble, because of the 

 approach of both fluids to the same condition. It 

 has been noted that a continual dilution of the liquid 

 towards which the endosmotic current was directed, 

 would tend to maintain the activity of the process ; or, 

 what is equal to the same thing, if a current of this 

 liquid flowed over the membrane this result would be 

 attained. Now the blood towards which the current 

 from the intestine sets is in continual circulation. It 

 no sooner receives by endosmosis solutions of sub- 

 stances from the stomach and intestines, than it whirls 

 them off in the current of the circulation, and a new 

 quantity of blood takes its place, maintaining the 

 degree of dilution that w r ill aid the process. But, 

 again, the process will go on with greater vigour, the 

 greater the extent of the animal membrane, or, more 

 properly speaking, the greater the surface of liquid 

 towards which the current is directed. 



Now this condition is fulfilled by the richness of the 

 vascular supply of the alimentary tract and by the 

 folds permitting o? increased extent of surface. 



The greater the difference that exists between the 

 liquids, the greater will be the speed and amount of 

 absorption by endosmosis. Thus, if a saline sub- 

 stance in the liquid food is very deficient in the blood, 

 its absorption, other things being equal, will be effected 



