49 



solulioii. (' ill' I- el,* who had the opportunity of trying 

 Ihcse alcohol |)i\'('ipilatc's in the culture, slated Ihal Ihey 

 increased Ihe rale ol' i^i'owlh nearly as much as the fresh 

 extract, a fact to wliich 1 also subscribe. 



Encouraged by these experiments, I attempted to develop 

 a method by which it could perhaps be ])ossiblc to frac- 

 lionize differenl proteins by alcohol precipitation. 



1 1 is known, that Ihe solution oi' colloidal system of 

 proleins is very unslable close to Ihe i.so-electric point. If 

 Ihe hydrogen ion concentration of the solution of a protein 

 is near Ihal of the isoelectric point of the protein, the 

 physico-chemical equilibrium is unstable and a very little 

 disturbance of any kind is able to bring about a precipi- 

 tation. Il is known from 1. oeb'^'^; Ihal al the iso-eleclric 

 point Ihe alcohol number is very low; i. e., a relatively 

 small amount of 95 jier cent alcohol is able to give a pre- 

 cipitation close lo the isoelectric point of the protein. At the 

 same lime as the alcohol number is at its minimum. Ihe 

 conductivity, osmotic pressure and swelling also attain a 

 minimum at the iso-electric point. 



II' we assume thai tlie body juices, in this case the em- 

 bryonic tissue juice and blood plasma, are built up of series 

 of more or less definite proleins with different iso-electric 

 points, we would expect, that at different hydrogen ion con- 

 centrations, we would be able to precipitate, by a certain 

 amount of alcohol those of the proteins which are nearest 

 Ihe iso-electric point at the given Ph. 



Experiments of this kind were made in the following, 

 way. Series of nine test tubes contained 5 c. c. each of 

 freshly prepared embryonic tissue juice. 5 c. c. of standard 

 buffei' solutions with different Ph. were added, so that the 

 extract-buffer mixtures all got a different hydrogen ion con- 

 centration, which varied from Ph. 5,6 to 7.5. To all of 

 these tubes were added 95 per cent alcohol in quanlities just 



*) Personal communication. 



