MAST CELLS IN CATTLE AND RAT 



Mast cells. Type-I cells accompany the main vessels of the arcades and 

 their lateral twigs, changing rather abruptly into type-II cells as the vessels 

 break up into capillaries. These type-II cells are scattered, singly or in pairs, 

 over the clear peritoneal window at various distances from the nearest capillary 

 and many of them show the imprint of connective-tissue fibrils. 



Omentum 



Vessels. As in the mesentery, the main vessels with muscle coats are 

 surrounded by a crenellated fatty sheath. However, in stained spreads the 



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Fig. 14 



This shows the bifurcation of a small blood vessel in a peritoneal fringe from one of the uterine 

 horns. The upper branch has along its outer wall a dense layer of mast cells seen as a solid 

 black line; the layer of mast cells in the adventitia of the upper aspect of the lower branch 

 seems to have become slightly dislocated from the vessel wall. Between the two branches the 

 mast cells are fanning out into the loose connective tissues, maturing, and then undergoing 

 degranulation (75). (Riley (1953), /. Path. Bad. 65, 461.) 



omental sheath can be clearly differentiated from that of mesentery by the 

 presence of darkly staining areas along its free margins and, to a less extent, 

 in the intervening peritoneum. These areas are the milk spots or 'taches 

 laiteuses' described by Webb (1931-32) in his study of peritoneal mast cells 

 in the rat (Fig. 15). A muscular branch from the main arteriole pierces the 

 fatty sheath to reach a milk spot and there breaks up into a leash of smaller 

 vessels. Having supplied the milk spot, the vessels are gathered together into 



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