70 COLLOIDS IN BIOLOGY AND MEDICINE t 



Thus it has been determined by the experiments of MARTIN H. 

 FISCHER on fibrin and of Wo. OSTWALD on gelatin that swelling is 

 much more strongly depressed by polyvalent cations than by mono- 

 valent ones (Mg < Ca < Ba < Sr < Cu < Fe) and it seems probable 

 that polyvalent cations counteract the action of monovalent ones in 

 favoring swelling. So far as I know there is as yet no colloid chemi- 

 cal confirmation of this assumption in the case of swollen colloids. 

 There are, however, a number of biological experiments concerning 

 the inhibition of the poisonous action of neutral salts by polyvalent 

 cations (see p. 378), which in all probability are referable to the in- 

 hibition of harmful swelling. According to these biological experi- 

 ments the antitoxic effect of cations increases with their valence and 

 stands in relation to the ionization pressure or the electrolytic solu- 

 tion tension. 1 



Our present knowledge indicates that the swelling and the shrink- 

 ing of hydrophile gels absolutely parallels the formation of ions and 

 neutral particles in the case of albumin. This has been more ex- 

 haustively discussed on page 153 et seq. The same factors which favor 

 the ionization of albumin, namely, acids and alkalies, also favor 

 swelling. In this case as in the other the presence of neutral salts 

 depresses the action of acids and alkalies, polyvalent cations or 

 anions acting more powerfully than monovalent ones. We rec- 

 ognize in both ionization and swelling a tendency towards an in- 

 crease of the free surface, which is associated with the taking up of 

 water. This may go so far that the molecules are split; hydrolysis 

 occurs and cleavage products are formed. Accordingly, chemical re- 

 actions, especially hydrolytic cleavages, occur much more rapidly 

 in swollen than in shrunken colloids. For instance (according to 

 E. KNOEVENAGEL*), the hydrolysis of swollen acetyl-cellulose by 

 potassium hydrate requires only a few minutes; but the same process 

 requires days in the case of the shrunken material. 



Non-electrolytes have only a slight influence on swelling. Of the few 

 cases known to us we may mention that urea favors the swelling of 

 gelatin even in acid solution, but it has no effect on fibrin. Alcohol 

 and sugar favor the swelling of gelatin in a certain concentration be- 

 tween 1 and 2 per cent. 



These data were almost exclusively obtained with gelatin and 

 fibrin. Both gels behave qualitatively alike (excepting with urea) 

 though there are quantitative differences. Fibrin swells much more 



1 To avoid any misunderstanding it should be stated that substances which 

 are themselves strongly toxic, e.g., barium, zinc or lead salts, may act in suit- 

 able small doses as antidotes (probably by counteracting swelling) to harmful 

 quantities of neutral solutions (e.g., pure NaCl solutions). 



