348 PHYSICAL PROPERTIES 



to the equilibrium which was disturbed. The occurrence of such 

 phenomena of hysteresis in heterogeneous systems containing 

 proteins, and their probable dependence upon the internal friction 

 of the solid phase have been commented upon in connection with 

 the heat-coagulation of proteins (Cf. previous chapter). 



I have shown that the films which are formed by gelatin around 

 chloroform droplets are permeable to alcohol and also, but less, 

 permeable to chloroform. The membranes are permeable to 

 various substances in the following order, those to which they are 

 most permeable being placed first, alcohol, ether, ethyl acetate, 

 scharlach R., chloroform, toluol, xylol, carbon bisulphide. 



The interesting observation has been made by Shorter (115) 

 that the surface-elasticity of freshly prepared protein solutions 

 undergoes a progressive increase with time. These increases are 

 not uniform but step-like, and represent, with irregular fluctua- 

 tion, the deposition of successive layers of molecular thickness. 

 Equilibrium is only attained with extreme slowness, a phenome- 

 non which Shorter attributes to the fact that in solutions an in- 

 crease in concentration of the protein at any point has a large 

 effect upon surface-tension but only a small effect upon the osmotic 

 pressure of the underlying layers of solution. In concentrated so- 

 lutions of protein, after a very prolonged period, it was found in 

 some cases that the progressive thickening of the surface-membrane 

 was suceeded by thinning. It is not certain, however, where such 

 long periods of time are concerned, that autohydrolysis of the pro- 

 tein may not have contributed toward modification of the results. 



The possible biological significance of protein films of this char- 

 acter has been discussed at some length in my communications 

 referred to above. 



11. The Specific Gravities of Protein Solutions. — We have 

 seen (Chap. XII) that the taking up of water by concentrated 

 proteins (gelatin) is accompanied by a volume-contraction (67); 

 hence in concentrated protein solutions the specific gravity cannot 

 be calculated directly from the specific gravities of the solvent and 

 solute respectively. 



The specific gravities of dilute protein solutions have been in- 

 vestigated by Haebler (38), Lehnstein (66) and others. According 

 to the latter author, the change in the specific gravity of a sodium 

 hydroxide solution due to the introduction of protein is directly 

 proportional to the percentage of protein introduced. 



