86 



Scientific Proceedings (32). 



Dreser,' Koeppe^ and others indicate that when they are carefully 

 freed from associated inorganic substances the cryoscopic depres- 

 sion due to dissolved proteins is negligible, while Reid ^ finds that 

 proteins purified by repeated recrystallization, resolution and re- 

 crystallization frequently possess, in solution,' no measurable 

 osmotic pressure ; and he concludes that provided every precaution 

 be taken to exclude impurities (among which he includes inorganic 

 constituents) from the protein solution it will be invariably found 

 to possess no osmotic pressure whatever and that the osmotic 

 pressures observed in solutions incompletely purified are due, not 

 to protein, but to the associated impurities. 



It appears to us that many of the above-quoted observations 

 and conclusions are vitiated by the fundamentally erroneous con- 

 ception that the inorganic constituents which are found associated 

 with proteins are invariably present as impurities and not in a state 

 of chemical combination. The manner in which this assumption 

 vitiates conclusions regarding the molecular weight (estimated from 

 the depression of the freezing-poirt or directly from the osmotic 

 pressure) of proteins will be clear from the following considera- 

 tions : Bases and acids have been demonstrated to form definite 

 salts of a constant composition with casein, serum globulin and pro- 

 tamin, and there can be no doubt whatever that similar compounds 

 are formed with other proteins. In solutions of casein and of 

 serum globulin it can be shown that as the neutral point is ap- 

 proached the alkali-binding power becomes less and from a variety 

 of data it can be shown that this phenomenon is due to a polymeri- 

 zation of the protein molecule according to equations of the type : 

 HXOH + HXOH = HXXOH + H^O* so that at or in the neigh- 

 borhood of the neutral point molecular aggregatesare formed of such 

 dimensions that, in the cases of the proteins mentioned, the solu- 

 tion assumes the character of a suspension and the protein is pre- 

 cipitated ; addition of acid or alkali shifts the equilibrium in the 

 direction of the lower complexes and the protein goes into solution 

 again in the form of a salt. Similar phenomena may be safely as- 



^ Dreser : Arch. f. exptr. Path, und Pharm., 1892, xxix, 314. 

 ^Koeppe : Arch. f. d. ges. Physiol., 1896, Ixii, 571. 

 3Reid: Journ. of Physiol., 1904, xxxi, 438. 



*T. Brailsford Robertson : Journ. of Physical Chem., 1908, xii, 473. 



