A Comparative Study of Several Samples of Neutral Rep and Their Effects on Paramoecium Caudatum

Several samples of neutral red have been studied; first, for the determination of their relative color intensities, and second, to determine their toxic effects on Paramoecium caudatum.

It was found that each of these dyes varied in physical characters both in dry form and in solution. The duration of life of groups of Paramoecia varied in each dye solution. These differences are probably due, at least in part, to differences in the chemical composition of each dye. This suggests that the varying results obtained by experimenters, in staining living material when using the same kind of dye under uniform conditions, may probably be attributed to these differences of chemical constitution of the dyes.

In the comparison of the toxic effects of the several samples most uniform results were obtained at concentrations of 1:5,000 and 1:10-000. At a concentration of 1:100,000 neutral red was found toxic but the results obtained were not in agreement with those obtained at lower concentrations.