The effect of some solutes on the velocity of the precipitin reaction.

K, Cs, Mg and Ca all reduce the velocity of the precipitin reaction relative to that observed in the presence of equal concentrations of Na. The nature of the anion in the medium affects the velocity even more strongly, the velocity being greatest in the presence of F and least in the presence of I. The inhibitory power of anions runs in parallel with their position in the lyotropic series. The polyhydroxy compounds sucrose, glucose, fructose, mannitol -inositol and glycerol also reduce the velocity of the precipitin reaction at concentrations of 0.3 M and higher. They also decrease slightly the amount of material that is eventually precipitated. Urea inhibits in a manner similar to the polyhydroxy compounds, but simple amides such as formamide, N-methyl-formamide and N,N-dimethyl-formamide are much more powerful inhibitors, so that inhibition can be demonstrated at concentrations as low as 0.02 M. An attempt is made to explain these effects in terms of known facts about the combination and precipitation of antigens and antibodies.