SYMPOSIUM ON COLLOIDS 



55 



sols is often spoken of as hydration, although this is strongly 

 condemned by Van Bemmelen as incorrectly emphasizing 

 chemical union of the water with the colloid. A great part of 

 the knowledge in this field we owe to the efforts of Martin 

 Fischer (14). The more significant facts known for gelatin 

 and fibrin are: acids, alkalies and urea greatly increase water 

 absorption; some anions of alkali metals increase water ab- 

 sorption (Rhodonate CI, Br, N0 3 .) and others decrease it 

 (S0 4 , P0 4 , Tartr., Citr.) (2: p. 43) ; salts in general inhibit 

 the hydrating effects of acids and bases and the total effect of 

 the salt is due to the joint action of the two ions; non-electro- 

 lytes show influence on the hydration effects of acids and alka- 

 lies ; sugar and other non-electrolytes reduce greatly the hydra- 

 tion effects of urea, while electrolytes show little influence. 

 Fischer finds these reagents act on the hydrophyllous colloids 

 of the body, especially the proteins of the cells and fluids, ex- 

 actly as they do upon gelatin and fibrin. He concludes from his 

 work that dropsy in the animal body is produced by the pres- 

 ence of agents that favor water absorption by colloids of the 

 body. Amongst these, acids and urea are the more important. 

 Intravenous injections of salts, alkalies and dextrose are ef- 

 fective in reducing edema by dehydrating tissues and fluids of 

 the body on the same basis as they act on gelatin and fibrin. 

 In fact he finds the cause and therapeutics of dropsy tied up 

 with w r ater absorption by body colloids. From this extensive 

 Work Fischer concludes that absorption by colloids and modi- 

 fication of it by various factors play the main part in water 

 relations and secretions in the animal body; w r hile osmotic 

 pressure is of very minor importance. This is a reversal of 

 the general view and brings colloids into prominence in con- 

 trast to crystalloids, which, although they act by the help of 

 colloidal semipermeable membranes, are the main source of 

 osmotic pressure. 



Whatever may be true in the animal, one who knows the very 

 extensive literature on the water relations of plants cannot 

 give osmotic pressure such a minor role there. It is probably 

 just as true that the significance of water absorption by col- 

 loids has been greatly underrated in plant physiology. This 

 is due to the over shadowing prominence given to osmotic 

 pressure and the resulting turgor pressure. We generally 

 think of the plant cell with its large vacuole and cell wall as 

 pre-eminently an osmotic machine. One is surprised when 

 Borowikow (15) announces that a root placed in .01 M. HC1 

 elongates twice as fast as in distilled water. It behaves much 

 like a piece of gelatin, although it ought to exhibit osmotic 



