THE MAST CELLS 



Fig. 26 



Mast cells in all stages of development are present in this section of solitary urticaria 

 pigmentosa; cytoplasmic granules are clearly visible. Many cells also show a juxta-nuclear 

 clear zone, indicative of the cell's immaturity. Toluidine blue ( 800). 



Courtesy Dr. J. M. Drennan. 



the results led us to suspect that mast-cell tumours are perhaps not quite so rare 

 as was formerly supposed (Nielsen, 1952; Head, 1953, 1958). 



Contact was first made with a number of veterinary surgeons in Scotland 

 and England. To those who agreed to co-operate, pairs of bottles were sent 

 containing respectively (a) a measured volume of 10 per cent trichloracetic acid 

 for a fresh, weighed sample of tissue for histamine assay, and (b) formol- 

 corrosive fixative for a small piece of tissue for histological confirmation of 

 the diagnosis. Despite our efforts, nearly two years elapsed before the first 

 mast-cell tumour was obtained. 



Three factors appear to have contributed to this initial failure to obtain 

 suitable material in addition to the acknowledged rarity of the tumours. The 

 first is that many of the specimens which are examined at veterinary centres 

 are submitted by outside practitioners: the tissue is often unfixed and there 

 may be considerable delay in transit. Secondly, by the time that a routine 

 pathological examination has been made and a diagnosis established, a further 

 7-10 days may have elapsed, by which time the gross specimen (even if retained) 

 is now useless for histamine assay. Thirdly, a histological diagnosis of mast-cell 



80 



