42 ON THE DIFFERENTIAL REACTION TO VITAL DYES EXHIBITED BY 



Protocol: Mouse 54-8, injected intraperitoneally with a 1 per cent solution of trypan blue 

 January 5 and 20, 0.5 c. c. each day; January 27, February 5, 10, 13, 17, 20, 24, 27, 

 March 3, 6, 10, 13, 17, 20, 23, 27, and April 10, 0.25 c. c. each day. 

 June 21: Animal is bright blue. Cells are full of dye visible with the low-power, but types are 

 not clear. Many cells with large deposits seen with this power under the oil prove to be fibro- 

 blasts and not macrophages. The two types are distinct on the whole. 



Macrophages are neither numerous nor striking and are easily overlooked. Their dye-content 

 varies from one or two small concretions in colorless vacuoles to several large, deep-blue vacuoles 

 and smaller deposits. They are rarely as deeply stained as the fibroblasts. 



Fibroblasts are well packed with regular, bright-blue granules, usually somewhat triangular or 

 linear, though often round and square. The size of these varies slightly in different cells, some 

 having so large vacuoles as to be identified as macrophages at first. Many possess also a single 

 mammoth deep-blue vacuole similar to those in macrophages. 



Dye deposits are, then, invariably more permanent in the fibroblasts than in 

 the macrophages, and time and again, after acute dye dosage which pigments 

 both types of cell, a period of freedom from dye treatment gives us at length areolar 

 tissue in which only the fibroblasts have retained their stain, while the macrophages 

 have lost their initially great content, due to the speedier decolorization undergone 

 by these cells. 



In an animal handled in this way, but now injected with a single high dose of a 

 positive azo dye, different in color from that first used, the macrophages of the 

 areolar tissue of the entire body exhibit their customary acute reaction and are 

 deeply tinged with the last vital color employed. If we examine the tissue quickly 

 during the interval preceding any appreciable dye deposition in the fibroblasts, 

 we may observe differential color-staining of the two cell types, the fibroblasts 

 carrying the earlier dye alone, the macrophages the dye last employed. 



Protocol: Mouse 58, injected subcutaneously with a 0.5 per cent solution of trypan blue, July 



27, 31, August 3 and 8, 0.5 c. c. each day; September 14, 21, 27, October 3, and 8, 5 



min. each day; October 16, 10 min.; October 20, 4 min. Injected intraperitoneally 



with a 2 per cent solution of dye T 148, December 1, 0.2 c. c. 



December 3: Low-power shows numerous cells filled largely with red (some blue) dye, contrasting 



with fibroblastic cells containing blue deposits. 



Under the oil, though it is somewhat difficult to identify all the red cells, the majority are seen 

 to be macrophages. These may, however, show large blue vacuoles or a blue tinge in red vacuoles. 

 Fibroblasts are usually closely packed with blue deposits, round and sharply linear in form. It 

 is true that on closer scrutiny some show pink threads and small pink vacuoles. In these 

 instances the pink threads are connected with blue dye deposits. Janus green shows filiform 

 mitochondria. 



It is remarkable that the majority of fibroblasts have not been affected by the red dye; also 

 that the majority of macrophages have no blue dye. 



It is interesting that this differential fading, or decolorization, which gives us 

 an actual subsequent predominance of the fibroblast stain, is also shown in the case of 

 vital-dye substances which from their colloidal nature decolorize slowly. In other 

 words, the differential behavior of the two types of cell is still evident, though a 

 longer period of post-experimental life is necessary before much decolorization 

 can take place. This is the case, for instance, in animals which are treated over 

 a time interval of about 75 days with afridol blue and allowed to decolorize dur- 

 ing a period of 90 days. (See Protocol, Mouse 57, page 41.) 



We have reserved for final consideration a further discussion of the peculiar 

 tendency of the segregation-apparatus of fibroblasts to assume a linear form. It is 



