THE MAST CELLS 



spreads. Ox liver capsule proved to be almost avascular, whereas small vessels 

 were comparatively common on the surface of the lung. In neither case, 

 however, were the mast cells disposed in relation to the vessels: the cells 

 immediately under the mesothelial surface of both organs seemed to have an 

 entirely random distribution. Paraffin sections of lung indicate that mast cells 

 often surround the subpleuval vessels: even here, the cells lie mainly in the 

 perivascular adventitia of the small vessels with muscle coats (Fig. 10). 



In some preparations mast cells appeared to be relatively common around 

 the subpleural lymphatics (Fig. 10). Further specimens of lung and liver were 

 therefore injected locally with a 1 per cent solution of the colloidal acid dye, 

 Evan's blue (T. 1824), in saline in the hope of demonstrating the lymphatics. 

 The injection was made immediately under the capsule and the area was then 

 massaged to spread the dye and force it into the lymphatic spaces. Examina- 

 tion of these spreads indicated that in general there is no more evidence of a 

 relationship of mast cells to lymphatics in ox liver capsule and ox pleura than 

 there is of their relationship to the blood vessels. The comparatively few 

 additional mast cells in the parenchyma of lung and liver which are seen in 

 paraffin sections are situated chiefly in the loose connective tissue surrounding 

 the bronchi and the portal tracts. 



A rather curious observation was made in the capsules injected supravitally 

 with Evan's blue. In addition to filling the lymphatics the dye often stained 

 faintly the mast granules themselves. Such staining does not occur in fixed 

 preparations. This suggests that the mast granule in the living state contains 

 an albumin component for which Evan's blue has a strong affinity, as it has 

 for the albumins of the plasma proteins: this may perhaps be the 'heparin 

 complement ' described by Snellman, Sylven and Julen (1951). The unexpected- 

 ness of the observation lies in the fact that the mast granules are among the 

 most intensely basophilic structures in the body, the only other known method 

 of staining them with an acid dye being that of Bujard (1930) in which mast 

 cells in paraffin sections treated with bromine can now be stained with acid 

 fuchsin. 



Mast cells are somewhat more obviously related to small blood vessels 

 in the dura mater, peritoneum, pericardium and tendon sheaths, though, 

 as in lung, they are more common around small vessels with a well-defined 

 adventitial coat than around the capillaries (Figs. 2, 3 and 4). 



If the search for mast cells in cattle had stopped at this point it might well 

 have appeared that the function of the mast cell is related to some property 

 common to serous membranes, perhaps to the formation of the mucinous 

 material which lubricates their surfaces. Such an hypothesis might also 

 account for the high mast-cell content of the synovial joints which develop 

 from clefts in the primitive mesenchyme. However, it appears less likely when 



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