258 PHYSIOLOGICAL PHYSICS. [Chap. xxn. 



conditions. The stream of the dilute solution would 

 carry off with it any salt that had passed out of the 

 osmometer, and would renew the contact of the mem- 

 brane with dilute fluid. It is of importance to note 

 this in the physiology of absorption. 



Where the solutions on different sides of the 

 membrane are of different chemical constitution, the 

 osmotic action depends on the chemical affinity of one 

 for the other. Thus the amount of action would be 

 greater between an acid and a base than between two 

 acids or two bases. 



If a galvanic current be passed through water, 

 provided with a porous diaphragm, in such a way that 

 the positive pole is on one side and the negative on 

 the other, the quantity of fluid will decrease 011 the 

 former and increase on the latter side. When the 

 current is passed through different liquids separated 

 by a membrane, it is capable of altering the results 

 according to its direction. Thus, when the current is 

 from water to a saline solution, it results in an in- 

 creased quantity of water passing into the salt ; when 

 it is reversed, an increased quantity of salt passes to 

 the water, and the volume of liquid will be increased 

 on the water side ; the endosmotic current, that is, 

 will be inverted. Sometimes, also, under the influence 

 of an electric current, there will pass through the 

 membranes substances which would be incapable of 

 passing through under ordinary circumstances. 



Crystalloids and colloids. Graham divided 

 bodies into these two classes, according to their 

 diffusive power. Thus, he found a class of substances 

 possessing this power, though in very different de- 

 grees, and capable of assuming the crystalline form, 

 and to this class he applied the term CRYSTALLOID. 

 On the other hand, there is another class of bodies, of 

 extremely low diffusive power, distinguished by their 

 absence of power to crystallise, by the gelatinous 



