MAST CELLS IN CATTLE AND RAT 



around the edge of the specimen, leaving the branching main vessels almost 

 clear of fat except for their immediate sheath of fibro-fatty tissue. Chains of 

 characteristic type-I cells occur in the adventitia of the main vessels with muscle 

 coats. Type-II cells are scattered around the capillaries or lie free in the loose 

 connective tissue near by. Where the perivascular tissues are lax the transition 

 from type-I to type-II cells can be clearly seen (Fig. 14). In some of these 





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Fig. 16 



Section showing (L to R) spleen, pancreas and loose subperitoneal connective tissue in the 

 rat. The mast cells are related to the loose connective tissue. Toluidine blue ( 116). 



fringes typical milk spots and smaller nodules of similar tissue are found 

 tucked away among the fat cells, and, where such tissue is present, mast cells 

 in all stages of development can be observed. 



Degenerate cells 



In spreads from all areas there are occasional type-II cells which appear 

 to be degenerating. The commonest sign of ageing is a generalized fading of 

 the metachromatic granules in the large type-II cells. In other cells this change 

 is accentuated by the presence of a few granules which stain exceptionally 

 deeply, giving the cells a characteristic punctate appearance. Other cells are 

 shrunken, the remaining granules lying near the periphery of the cell, in the 



55 



