THE TWO GREAT GROUPS OF CONNECTIVE-TISSUE CELLS. 33 



employment of any azo dye and show characteristic differences, depending upon 

 the type of dye used. This evidence is furnished in the most striking way by the 

 behavior of fibroblasts after dosage with what we have called "negative," or non- 

 diffusible, vital dyes. After subcutaneous injections with any of the large existing 

 series of such compounds, the fibroblasts several centimeters removed from the injec- 

 tion site accumulate only the minute fibroblastic "dye bodies," which we in our 

 paper with Schulemann and in common with Kiyono, Tschaschin, and others, have 

 already described (fig. 33). Such is not the case, however, with the fibroblasts in 

 the immediate vicinity of the site of injection and is never the case with fibroblasts 

 at the actual point of injection. In all such locations, where much more dye sub- 

 stance has had access to the fiber-forming cells, the latter ingest greater quantities 

 of the dye, never as great, it is true, as the macrophages in the same location, but 

 so great that one may meet over a considerable territory fibroblasts whose proto- 

 plasm is completely filled with a vacuolar segregation-apparatus which is devel- 

 oped in direct response to the need of housing the vital dye (see fig. 72). 



Protocol: Rat 200, injected subcutaneously with a 1.5 per cent solution of isamine blue 

 March 15, 19, 22, 26, 29, April 2, 5, 9, and 12, 1917, 1 c. c. each day. 



1918, March 21: Examined subcutaneous tissue from back (area of injection). Animal is 

 stained a light greenish blue over the back. Subcutaneous tissue is bright blue in this area. Under 

 the low-power, cells showing a high content of light-blue dye deposits are seen, but cell types are 

 not distinct. 



The oil shows the same difficulty in identifying cell types. The majority of fibroblasts are 

 large cells, sometimes with two nuclei, whose cytoplasm is crowded with small, bright-blue deposits 

 rather uniform in size and tending to be angular. Neutral red stains these vacuoles and discloses 

 no new structures. The extent of cell processes filled with dye deposits is often very great, and 

 apparently there is little or no cytoplasm free from dye (fig. 72). 



Macrophages can be identified by their general morphology (shape of cell, size of nucleus, etc.) 

 rather than by any peculiarity of their dye deposits, since these are very similar in size and number 

 to those of the fibroblasts, though more often round. Near blood-vessels the macrophages are full 

 of deep-blue vacuoles, some of which are large. In areas away from the injection-point these cells 

 have vacuoles which are smaller on the whole and much fainter than those in fibroblasts and do not 

 fill the cells as completely. 



The fibroblasts of the serous membranes in cases of large and long-continued 

 peritoneal injections, even with the negative as well as the positive azo dyes, show 

 this great multiplicity of "dye bodies" in a most striking way. 



Just as the fibroblasts in the case of the subcutaneous injection of a negative 

 dye show great differences in their segregation-apparatus in strict accordance 

 with their distances from the injection-point, so also do these cells exhibit more 

 accurately than do the macrophages characteristic differences in the form and 

 extent of the apparatus, depending on the physical properties of the particular 

 vital dye. Compare, for instance, the typical trypan-blue deposits in the fibro- 

 blasts shown in figure 59 with the typical dye T 148 deposits depicted in figure 82. 

 In the investigation of a long series of azo compounds it has been possible to dis- 

 cover dyes whose facility in entering the fibroblastic protoplasm is so great as to 

 establish here an extensive vacuolar segregation-apparatus which has few or none 

 of the peculiarities (minute size, irregular, angular, and filiform morphology) 

 which with most vital dyestuffs characterize these cells. The discovery of dyes 



