The Coagulation of Protein by Sunlight. 245 



observation of Corin and Ansiaux(ll) that if freshly coagulated egg albumin 

 be vigorously shaken it is again dispersed and a clear solution results. This 

 point is discussed under the theory of the whole phenomenon. 



The effect of adding various substances was tried on the serum albumin 

 solution, and control tubes were prepared in each case and kept in the dark 

 at the same temperature. Electrolytes in moderate concentration were found 

 to increase the rate of denaturation, e.g., NaCl, (NH^SO^, KSCN. Traces of 

 alcohol, acetone and toluene did likewise. Glucose and ether had no apparent 

 effect. To be in a position to study the effect of various substances, however, 

 on the rate of coagulation, a quantitative method would have to be devised. 

 From the above experiments it would appear as if any substances with 

 dehydrating power would increase the rate of denaturation. I am at present 

 working upon this subject. 



The Nature of the Light Reaction. 



From the foregoing experiments it will be apparent that the reaction 

 brought about by sunlight is very similar to heat coagulation, if not identical 

 with it. The main facts associated with the phenomenon of heat coagulation 

 may be briefly summarised for purposes of comparison. Chick and Martin (12) 

 have conclusively demonstrated that, under certain circumstances, i.e., when 

 the water present is in large excess and the hydrogen ion concentration is 

 kept constant, the reaction can be proved to be of the monomolecular order. 

 The reaction is between protein and water and the effect of temperature is 

 merely to accelerate it. It has an extraordinarily high temperature coefficient 

 and the velocity is influenced by a number of conditions, especially acid and 

 alkali. During coagulation, if the reaction be on the acid side of the iso- 

 electric point, hydrogen ions are removed from solution ; if the reaction be on 

 the alkaline side hydroxyl ions are removed. The degree of removal of the 

 H or OH ions is dependent on the total concentration of acid or alkali and the 

 Ph of the solution. Heat coagulation of albumin consists of two processes : 

 (1) a reaction between protein and water (denaturation); (2) the separation 

 of the altered protein in a particulate form (agglutination). From the 

 investigation of Sorensen and Jiirgensen (13) on ovalbumin, and of Michaelis 

 and co-workers (14) on serum albumin, the maximum flocculation of denatured 

 protein has been demonstrated to occur only at its isoelectric point. It is 

 interesting to note here that Michaelis and Davidsohn (15) have found that 

 the isoelectric point of denatured serum albumin (Ph 5 - 4) is not the same as 

 natural serum albumin (Pa 4-6). Hardy (16) recognised 'the double nature of 

 heat coagulation of egg white as long ago as 1899 and considered the primary 

 change as one of an emulsoid colloid to a suspensoid type, which was readily 



