144 PHYSICAL CHEMISTRY IN MEDICINE. 



protein in even very dilute solutions ? All these salts are 

 characterized by the fact that they undergo great hydro- 

 lytic dissociation in dilute solution in other words, take 

 up water and break up into their metallic hydroxide and 

 their acid. According to different investigations which 

 agree in their conclusions, the dissolved colloidal electro- 

 positive metallic hydroxide is the real protein-precipi- 

 tating constituent. If now it is true that colloids mutually 

 precipitate each other only through the opposite electrical 

 charges which they carry, then the uncharged protein 

 should in general not be precipitable through electro- 

 positive heavy metals. It can be easily shown that our 

 uncharged protein, in contrast to native protein, cannot 

 be precipitated through salts of Fe, Cu, Hg, Pb, and Zn. 

 This experiment harmonizes, therefore, with BILLITZER'S 

 theory, according to which protein is very stabile in the 

 uncharged state. 



Let us now turn to something else. As is well known, 

 alcohol is an excellent precipitant for proteins. Since 

 alcohol as a non- electrolyte furnishes practically no ions 

 in aqueous solution, its precipitating power cannot rest 

 upon electrical grounds. The matter may be explained 

 in the following way : Proteins are not soluble in alcohol, 

 but they are readily miscible with water. The proteins 

 are therefore crowded out of their solvent through the 

 addition of much alcohol, in the course of which their 

 small particles, by virtue of their surface tension, coalesce 

 into larger aggregates in a way similar to the clumping of 

 the particles of a fresh, fine precipitate into larger masses 

 with time. We will therefore not be surprised to see 

 that our uncharged protein is readily precipitated by 

 alcohol. But what will happen if we first give this protein 



