ON HEAT COAGULATION OF PROTEINS. 285 



Experiments with egg albumen gave analogous results. In both 

 cases there is only a narrow range within which aggregation of the 

 denaturated particles occurs (optimum acidity of Michaelis and Rona). 

 With too much or too little no agglutination occurs. The fact that 

 the weakest acid gave the largest range suggested that the phenomenon 

 was conditioned by acidity rather than acid added. 



On repeating the experiments with determination of hydrogen-ion 

 concentration this was shown to be the case. The range of acidity 

 corresponding to complete agglutination was with all three acids the 

 same (0'5 to 15 x 10 - 5 normal). 



The effect of salts upon agglutination. 



The effect of salts (NaCl, Am,So 4 , Na 2 So 4 ) upon the agglutination 

 of denaturated egg albumen and serum albumen is the exact opposite. 

 Whereas the presence of salts facilitates the agglutination of the particles 

 of altered egg albumen, it disperses those of serum proteins. 



The agglutinating effect of acidity, salt content, &c, can be most 

 conveniently studied in solutions of egg albumen or serum proteins 

 which have previously been boiled in their natural reaction. Subse- 

 quent adjustment of the acidity or salt content brings about agglutina- 

 tion and complete precipitation of the proteins. Using such material 

 we have estimated the influence of salts upon the velocity of agglutina- 

 tion by determining the time taken for visible particles to appear 

 at 37° C, taking the reciprocal of this time as an index of agglutina- 

 tion rate. 



Employing this method it was found that concentration of NaCl 

 up to 0T per cent, exerts little effect, but beyond this the effect 

 becomes very marked. With serum albumen the rate of agglutination 

 is progressively lowered, and with egg albumen progressively increased. 



Effect of temperature on agglutination rate. 



The effect of temperature is peculiar. For each particular con- 

 centration of salt and acidity there is a critical temperature below 

 which agglutination does not occur. As the temperature is increased 

 the rate rises very greatly at first, and then less and less until at tem- 

 peratures well removed from the critical one the influence of rise in 

 temperature is consistently to multiply the rate two to three times per 

 10°C. 



Theoretical considerations regarding the above facts concerning 



agglutination. 



Whether particles cohere depends primarily upon their curvature 

 (size) and the magnitude of the surface tension between them and the 

 solution. The electric condition of the particles is also of importance, 

 not only because, if these are charged, the surface tension is dimin- 

 ished (Helmholtz-Bredig effect), but because the possession of a charge 

 of like kind leads to repulsion. This force of repulsion must be over- 

 come before the particles can be brought sufficiently near one another 

 for surface action to be effective. 



