In continuation of the observations on vital staining by means of phthalein indicators, reported in a previous paper, some members of the group with acid ranges have been employed. The results accord closely with those already obtained, in pointing to the existence of characteristic differences in the reaction within the organs. Roughly speaking, these latter fall into two groups. Within the members of the one a noteworthy acidity would appear to prevail, whereas in those of the other acidity seems slight at most, and in a few instances signs of a faint alkalinity are to be met. In general the "acid" organs are such as have a great metabolic activity whereas the "neutral" group manifest but an inconsiderable one. All of the tissues examined seem to be relatively acid compared with the blood plasma. The findings with the phthaleins as a group are discussed.