THE MAST CELLS 



tumour will be missed if only the standard haematoxylin-eosin routine is 

 used since the mast granules fail to stain by this method. This must have 

 happened often in the past. However, as Nielsen (1952) emphasizes, an 

 immediate diagnosis can be reached by making an imprint of a fresh slice of 

 tumour on a microscope slide and staining this, as a blood film, either with 

 the Giemsa stain or merely with a drop of 0-1 per cent toluidine blue. This 



Fig. 28 



Paraffin section of dog mastocytoma. Rounded densely-staining mast cells set in a coarse 

 collagenous stroma. Toluidine blue ( 416). 



simple method of screening tumours in veterinary practice would no doubt 

 disclose many mast-cell tumours which would otherwise be overlooked (Fig. 27). 

 Results. The first dog mastocytoma was sent to us in August 1952 by Mr. 

 E. Cotchin, M.R.C.V.S., of the Royal Veterinary College and Hospital, London, 

 the specimen being part of a tumour from the right axilla of a five-year-old 

 female Boxer dog. The tumour had been excised by an outside practitioner, 

 and there was some delay before a weighed portion of tissue was placed in one 

 of our containers of trichloracetic acid pending further laboratory examination. 

 Histologically the tumour was found to consist of a coarse collagenous frame- 

 work enclosing islands of cells which stained deeply and metachromatically 

 with toluidine blue and with the Giemsa method, though individual cytoplasmic 



82 



