THE RELATIVE REACTION WITHIN LIVING MAMMALIAN TISSUES. V. (b) INrr.OrNCr or Lnn'mINSOLtrBLE TIsstm MATERr~LS ON a~m SIGNIFICANCE OF THE COLORATION WITH SOW

In a microscopic study of living tissues stained with the phthaleins one sees no sign that the coloration is due to accumulation of the indicator upon special cytoplasmic substances. I t is true that under certain circumstances a segregation of phthalein within cell vacuoles may occur; 1 but ordinarily the staining appears diffuse, and only in the case of bone ceils and cartilage cells do the findings suggest that there may be some deposition of dye upon the cell surfaces. But needless to say, the evidence of the eye is not conclusive in this matter; nor can it even be deemed of much value when one considers the fact that phenol red is removed on occasion from the field of action as an indicator by proteins in solution. The experiments with tissue extracts described in an accompanying paper s may perhaps be taken as constituting a partial check upon the influence of this removal factor upon the colors exhibited by tissues. They tell nothing, however, of the possibility of errors due to an accumulation of phthalein upon tissue materials insoluble in lymph, salt solution, or water. True, such materials were doubtless present in suspension in our turbid preparations, but only in small quantity. To learn something of the partition of the phthaleins between extract and tissue residue an experiment was performed as follows: