502 EXPERIMENT STATION RECORD. 



" The influence of acids and alkalis on denaturation-rate is compared witli 

 their effect on the viscosity and precipitability by alcohol of protein solutions 

 and upon the imbibition of water by protein. It is suggested that protein in the 

 form of salts is in more intimate association with water." 



On the " heat coagulation " of proteins. — IV, The conditions controlling 

 the agglutination of proteins already acted upon by hot water, Harriette 

 Chick and C. J. Martin (Jour. Physiol., 45 (1912), No. 4, pp. 261-295, figs. 7).— 

 The dispersion of denatured proteins by small amounts of acid or alkali is 

 attributed to the electrical charge given to the particles. This charge, if 

 neutralized, renders the proteins isoelectric. With the solution agglutination 

 takes place. 



" In common with other observers, we find that reaction of the solution is 

 the principal factor in determining the degree of agglutination of denatured 

 proteins. The optimum acidity for precipitation in absence of electrolytes 

 is found to be at a concentration of hydrogen ions equal to about 3X10-6 

 normal in case of the denatured protein of both serum and egg-white, thus 

 confirming the figure obtained by Michaelis and Rona for the isoelectric point 

 of serum-albumin. 



" Agglutination is greatly influenced by the presence of neutral salts. Their 

 action is twofold: (a) Alteration of the reaction of protein-containing solutions. 

 The concentration of hydrogen ions is lowered in acid solution and that of 

 hydroxl ions in alkaline solution; (b) neutralization or increase of the electric 

 charge carried by the protein particles, according as the charge on the protein 

 is of opposite or similar sign to that carried by the more potent ion of the 

 salt. 



" In the case of egg white agglutination of the denatured protein is assisted 

 by the addition of electrolytes and the range of hydrogen ion concentration over 

 which agglutination occurs is extended. In the case of serum proteins, a similar 

 result is obtained only when salts are present in very low concentration; in 

 presence of more concentrated electrolytes agglutination is hindered if not 

 altogether prevented. 



" The cause of dispersion by salts appears to be the absorption of ions by 

 the denatured particles of protein. If the chai'ge of the more potent ion is of 

 opposite sign to their own charge they will, after being first discharged, become 

 recharged with a sign opposite to that they originally carried. The effect is 

 increased with higher valency. Denatured serum protein is easily dispersed 

 by electrolytes, but with egg albumin dispersion accompanied by reversal 

 of charge was detected only after the addition of sodium citrate. In the case 

 of dispersion by divalent cations such as Ca we were not able to demonstrate 

 the existence of any chax-ge on the dispersed particles. 



" For every solution containing denatured protein there is a critical tempera- 

 ture, depending on the reaction and on the concentration of protein and electro- 

 lytes, below which agglutination does not take place. Immediately above 

 this critical point rise of temperature has at first a very marked effect in 

 enhancing the rate of agglutination ; this influence, however, becomes less 

 and less until, at temperatures far removed from the critical temperatures, 

 the effect is consistent, agglutination rate being increased about two to five fold 

 per rise of 10° C. An explanation is suggested. 



" No support is found for the conclusion both of Starke and Mill that 

 albumin, when heated in alkaline solution, is converted into globulin ; between 

 (a) the dispersed protein and (b) the coherent precipitate obtained on heating 

 in alkaline and faintly acid solutions, respectively, there appears to be no differ- 

 ence which can not be accounted for by the different state of aggregation. 

 Reasons are adduced for regarding the substance studied by these observers aa 



