The influence of lymph-insoluble tissue materials upon the colors manifested by phthalein indicators has been tested by comparing the hue of sections of various organs, stained by immersion in colored lymph, with the hue of the surrounding fluid. The reaction has been brought to approximate that of life by a greater or less saturation of the material with carbon dioxide. No evidence has been obtained of indicator errors referable to the association of the phthaleins with tissue substances.
The inferences to be derived from the experiments, and from others detailed in a preceding paper, are discussed. The results of them all are in essential agreement. They demonstrate that the observed hues in tissues vitally stained with phenol red, brom cresol purple, and chlor phenol red cannot be laid to indicator errors resulting from an association of the phthalein with tissue materials. The fact is of special note in connection with organs which exhibit, when stained, the colors indicative of an outspoken acidity.
The findings constitute a control upon the influence of the tissue materials on the colors manifested by the phthalein indicators when used as vital stains; but they leave untouched the problem of the influence of tissue activities upon the coloration.