PROPERTIES. 97 



divided 1 and the same applies to the question as to manner of heat 

 coagulation and the conditions under which it takes place. 



The heat coagulation of a protein solution is dependent upon the hydrogen 

 ion concentration of the solution. According to MICHAELIS and co-workers 

 the optimum of the hydrogen ion concentration falls in the coagulation of a 

 protein solution (precipitation of the modified protein) with the isoelectric point 

 of the solution and the optimum of the flocking is not changed in regard to the 

 hydrogen ion concentration by changes in the protein concentration. According 

 to SORENSEN and JuRGENSEN, 2 on the contrary the optimal hydrogen ion con- 

 centration is the same as contained in a solution of the pure protein in pure 

 water caused by the electrolytic dissociation of this protein and is therefore 

 independent of the protein concentration. This hydrogen ion concentration, 

 according to these workers diminishes during the heat coagulation which they 

 consider as a proof of the diminution in the protein concentration of the solution. 



A modification can be brought about also by the action of acids, 

 alkalies, or salts of the heavy metals, in certain cases by water alone, 

 and also by the action of alcohol, chloroform (SALKOWSKI), and ether, 

 by violent shaking (RAMSDEN 3 ), etc. 



An adsorption of proteids by a suspension colloid such as silicic acid, 

 colloidal ferric hydroxide and kaolin, can easily take place, and indeed the 

 proteid of a solution can be removed by the use of colloidal ferric hydrox- 

 ide or shaking with kaolin (RoNA and MICHAELIS 4 ) . That the proteids 

 can serve as preventives in the precipitation of suspension colloids has 

 been mentioned in Chapter I. In the same manner a mastic suspension 

 is protected from the precipitating action of an electrolyte by an excess of 

 a proteid solution, while the reverse may be brought about, namely, a 

 proteid solution can be precipitated by a large quantity of mastic emulsion 

 in the presence of a proportionately small amount of electrolyte. The 

 method for the removal of proteid from solutions, as suggested by 

 MICHAELIS and RoNA, 5 is based upon this behavior. 



We have already discussed in Chapter I the electric charge of the 

 proteins under various conditions and the migration of these in electric 

 fields of currents. 



1 See Halliburton, Journ. of PhysioL, 5 and 11; Corin and Berard, Bull, de 1'Acad- 

 roy. de Belg., 15; Haycraft and Duggan, Brit. Med. Journ., 1890, and Proc. Roy. 

 Soc. Edin., 1889; Corin and Ansiaux, Bull, de PAcad. roy. de Belg., 21; L. Fredericq, 

 Centralbl. f. Physiol., 3; Haycraft, ibid., 4; Hewlett, Journ. of PhysioL, 13; Duclaux, 

 Annal. Institut Pasteur, 7. In regard to the relationship of the neutral salts to the 

 heat coagulation of albumins see also Starke, Sitzungsber. d. Gesellsch. f. Morph. u. 

 Physiol. in Munchen, 1897; Pauli, Pfliiger's Arch., 78. 



2 See Ergeb. d. PhysioL, 12 which contains the pertinent literature. 



3 See Salkowski, Zeitschr. f. physiol. Chem., 31; Fr. Kriiger, Zeitschr. f. Biologie, 

 41; Loew and Aso, Bull. Coll. Agric., Tokio, 4; Ramsden, Zeitschr. f. physik. Chem., 

 47 and Arch. f. (anat. u.) PhysioL, 1894. 



4 Biochem. Zeitschr., 5. 



6 Biochem. Zeitschr., 2, 3 and 4. 



