SOAPS, PROTEIN DERIVATIVES AND TISSUES 



219 



The notion that solution is but a contin- 

 uation of swelling persists to this day. 1 

 Investigation 2 of the problem, however, 

 has shown that this is not the case. The 

 matter is easily proved by working with 

 gelatin at concentrations and tempera- 

 tures near its gelation or melting point. 

 Since alkalies and acids increase hydra- 

 ti<>n (increase swelling) the addition of 

 these substances to a barely liquid 

 gelatin-water mixture ought to stiffen it. 

 As a matter of fact just the reverse occurs. 

 By working with a stiff gelatin, a pre- 

 viously solid mixture is made to liquefy 

 upon the addition of these substances. 



The phenomena of swelling (hydration) 

 and of " solution " 3 in such soluble protein 

 gels as gelatin, while frequently associated, 

 are therefore essentially different. Swelling 

 is best understood as a change whereby the 

 protein enters into physico-chemical com- 

 bination with more of the solvent (water), as 

 a change in the direction of greater solubility 

 of the solvent in the protein; " solution " 

 is best conceived of as a change in the direc- 

 tion of greater solubility (an increased degree 

 of dispersion) of the colloid in the solvent. 

 If reference is made to Figs. 48 and 49 

 (page 70) it will be noted that changes 

 involving swelling occur in the region 

 In-low the level marked V; changes in 

 the direction of liquefaction or " solu- 

 tion " above the level marked F. A 



I 8ec for example WOLFGANG PAULI: Kolloidchomic der Eiweisskorper, 

 63, Dresden (!'.'. 



MUMIN II FIBCHER: Science, 42, 223 (1915); Kolloid-ZciUs. In . 17. 1 

 (1915). 



'Since there are many opinions rc^mlm^ tin- nature of "solution. 

 rate definition of the term is not easy. We are here using tin- t< mi in its 

 broadest sense as covering everything, in tin- (:*< of tin- <-o||..j<ls. from tlirir 

 tiMii | ...i tit upwards to the accepted "true" solution of the physical 

 chemist*. 



