Precipitin Reaction: II. Effect of Certain Electrolytes on the Formation of Precipitates

Abstract

In the first paper 1 of this series, Downs and Goodner showed the inhibitory effect of various sugars on the precipitin reaction. Although many other factors governing this reaction have been investigated, the effects of a comprehensive series of salts at various concentrations on the formation of a specific precipitate have not been reported in the literature, and it seemed worth while to undertake a study of this type. It was established by Hirsch 2 that precipitation can occur over a fairly wide range of hydrogen ion concentration, from pn 6 to pH 9.4, although the maximum precipitation occurs near the acid end of the range, that is, near the iso-electric point of the proteins in the antigen and antibody. He found that although precipitation was inhibited above pn 9.4, and although nonspecific precipitation occurred below pn 6, neutralization of the mixtures restored the ability to give specific precipitates. De Kruif and Northrup 3 emphasized the importance of both potential difference and cohesive force in the agglutination reaction. According to them, whenever the potential difference between the sensitized bacteria which they were studying and the surrounding liquid was reduced below about 15 millivolts (either positive or negative), agglutination occurred unless the cohesive force was simultaneously decreased. They found the cohesive force to be unaffected by salts in concentrations lower than thousandth normal, and consequently below this limit agglutination occurred whenever the potential difference was reduced