THE MAST CELLS 



All compounds were made up fresh in pyrogen-free distilled water, and a 

 standard volume (1 ml.) of solution was employed for each injection. 



Doses of the more toxic compounds (diamidines and curare) were chosen 

 experimentally to produce (a) death of a 200 g. rat in 5-10 seconds or (b) a 

 survival time of about 3 minutes, depending on the speed with which the 

 intravenous injection was given. Thus the histamine-liberators themselves 

 were used to halt the train of events in the tissues and permit the material to 

 be examined at various stages of the shock which had been induced. This 

 method had the further advantage with the fluorescent diamidines (stilbamidine 

 and 2-hydroxy stilbamidine) of ensuring that sufficient diamidine was present 

 in the tissues for its detection in fresh tissue spreads examined in ultra-violet 

 light. With the less toxic compounds (diamines and peptone) the experimental 

 animals were killed by a blow on the head at appropriate intervals after 

 injection. 



Preparation and staining of tissues. Immediately after the experimental 

 animal had been killed, spreads of subcutaneous connective tissue, mesentery, 

 omentum and other peritoneal fringes were prepared as previously described. 

 If fluorescent histamine-liberators had been used the fresh spreads were first 

 examined microscopically in ultra-violet light from a Hanovia diagnostic 

 lamp with a Wood's glass filter directed obliquely downwards on to the surface 

 of the spread. Thereafter these and all other spreads were fixed in 80 per cent 

 alcohol for at least twenty-four hours before being stained with 1 per cent 

 aqueous toluidine blue or methylene blue for mast cells. 



Results 



Fluorescent histamine-liberators 



Group a. Rapid injection. Fresh peritoneal spreads from animals killed 

 by rapid (5 sec.) injection of lethal doses of stilbamidine or 2-hydroxy stil- 

 bamidine were examined microscopically under direct ultra-violet light (Fig. 19). 

 Against a dark background, or at most a faint autofluorescence from the fat 

 globules, one sees numerous bright, sharply defined fluorescent spots situated 

 predominantly near small blood vessels. With stilbamidine the spots are 

 a steely blue-grey; with 2-hydroxy stilbamidine, a more golden colour. Occa- 

 sionally the whole vessel seems to fluoresce, presumably from its content of 

 diamidine, or the vessel wall alone is visible in a pale violet tint. The remaining 

 vessels appear as dark lines. If 1 per cent toluidine blue in saline is now run on 

 to the preparation the fluorescence immediately disappears. The section is not 

 moved, but visual light is now transmitted through the specimen, and it is seen 

 that where the fluorescent spots were situated there are recognizable tissue 

 mast cells (Fig. 20). The correspondence in size and position is very exact 



60 



