ED\\T:N JOSEPH COHN 



707 



these cases was ammonia, and was determined in the manner described by 

 Sorensen (13), in the filtrate and washings from globulin coagulated by heat at 

 its isoelectric point. It is therefore possible that the very small excess of ammonia 

 reported was due in part, or in whole, to the splitting of ammonia from the protein 

 molecule. That this is involved in the coagulation of proteins by heat is ren- 

 dered probable by the investigations of Sorensen and Jurgensen (38) on albumins, 

 and by the observation that such proteins as casein and glutenin, which are very 

 slightly soluble at their isoelectric points are not heat-coagulable. The alter- 

 native possibility is that serum globulin is capable of combining with a certain 

 amount of base even at its isoelectric point. This will be the subject of another 

 communication. In Table I are collected the ammonia concentrations in the 

 serum globulin preparations that have been studied thus far, and also the hydro- 

 chloric acid that was required to bring them to the isoelectric point. 



TABLE I. 



Analyses of Serum Globulin Preparations. 



* Serum Globulins I and II were prepared in collaboration with Professor 

 Sorensen at the Carlsberg Laboratorium in Copenhagen, early in 1920. They 

 were prepared as ammonium compounds and were not brought to the isoelectric 

 point. The data that are given are derived from certain experiments in which 

 the protein was brought to the isoelectric point in order to study the solvent 

 action of neutral salts. The method of further purifying globulin at its iso- 

 electric point was subsequently devised. 



Stirring was always continued for many hours after the isoelectric 

 point was reached, in part to break up the flocks or aggregates that 

 form under these conditions, and to prevent the occlusion of impuri- 

 ties in them, in part to hasten the attainment of equilibrium in so 

 sluggish a system. Occasionally it has been found necessary to break 

 the larger aggregates with a pestle and mortar. The protein was 

 finally returned to the cold room, from which it was never removed for 



