THE TWO GREAT GROUPS OF CONNECTIVE-TISSUE CELLS. 5 



great group of vital acid-azo dyes. Under the segis of Ehrlich's notions, we saw 

 unique advantages in the analyses of the relation of chemical constitution to bio- 

 logical effect in these numerous compounds, and, above all, an opportunity to track 

 out in this way the underlying nature of the vital-staining reaction. f We have 

 announced in preliminary papers our conviction that the magical staining effect 

 whereby trypan blue and its dye relatives mark out certain cells and tissues, leaving 

 others unaffected, is only a phenomenon of elective storage. We have stated that 

 the phenomenon has affinities with the well-known phenomenon of phagocytosis, 

 not only by virtue of the fact that the cells which stain most intensely (macrophages) 

 are all true phagocytes, but also because both with large particles and with dye 

 molecules we have an ingestion and storage of foreign material on the part of the 

 cell. Yet vital staining with the azo dyes differs from phagocytosis in the fact that 

 in the former phenomena the physical dimensions of the particles ingested all fall 

 in the ultra-microscopic realm and indeed — by virtue of their variable, but often 

 marked, powers of diffusion — cross the imaginary boundary which Graham set up 

 to separate crystalloids and colloids. This viewpoint is best expressed in the recog- 

 nition that in vital staining with the trypan dyes a segregating and concentrating 

 mechanism is possessed by the protoplasm of all vitally stained cells, as well as a 

 mechanism by virtue of which coarse particles (phagocytosis) or excessively minute 

 ones (dypsocytosis) may be taken inV 



However perfect the ability of stains to diffuse into living protoplasm, there 

 must also be a segregating and concentrating mechanism at work or their presence 

 within the cell will not gain any emphatic exhibition as "vital" granules. Ample 

 demonstration of this is shown, for instance, by the epithelial cells of the mammary 

 gland, which may secrete into the milk of mother rats enough of certain dyes to 

 deeply color the intestinal contents of the suckling young and yet no deposits occur 

 in the gland-cells through which the dye molecules have with certainty passed. 1 

 Our conclusions, indeed, run sharply counter to those proclaimed by Fischel, Gold- 

 mann, and others, who would have preferred to see in all vital staining an elec- 

 tive tingeing of integral protoplasmic constituents or cell organs; but they rest 

 on the confirmatory evidence of the most careful cytological studies on material 

 in which many dye substances and the most various dosage have been employed. 

 They have, furthermore, been accepted by those who have recently tested them 

 either by the use of experiments or of an especially advantageous material, as 

 attested by the conclusions of Kiyono in his second paper, Downey, McClure, and 

 E. L. and E. R. Clark. This paper, concerned solely with the behavior of the 

 connective-tissue cells, rests to a great degree on the experiments of the last few 

 years prosecuted for the sake of the other and more general end, and will have to 

 antedate the larger publication by stating its main conclusions, at least so far as 

 they bear on the interpretations which we present. A personal and peculiar con- 

 cern of Professor Mall, who from the beginning aided with more than sympathetic 



1 According to the studies of Sutter in this laboratory, this is the case, for example, with dianil blue 2 R (1 molecule 

 ortho tolidine diazotized and combined with 1 molecule Neville-Wiuther acid and 1 molecule of chromotrope acid), but it 

 does not hold for trypan blue, where mammary epithelial deposits are the rule. 



