THE MAST CELLS 



small vessels at the periphery of the area standing out distinctly owing to 

 swelling, proliferation and increased staining of their adventitial cuffs. Ad- 

 jacent fibroblasts also are often well stained and of bizarre shape. 



A curious fact was noted in these animals. Both in the subcutaneous 

 connective tissue and in the ears, the mast cells appear to escape entirely the 



Fig. 35 



' Subacute dosage ' experiment. Omentum at day eleven, showing alternative ways in which 

 the mast-cell population is restored after depletion by a histamine-liberator. The big cells 

 are refilled ' ghost ' cells. In addition, small new cells are forming from the adventitia 

 of blood vessels and the septa of fat cells, as well as from scattered precursors in the loose 

 connective tissue. Toluidine blue ( 450). (Riley and West (1955), /. Path. Baa. 69, 269.) 



effects of the histamine-liberator if they lie in the perineurium of the peripheral 

 nerves. Indeed, these nerves can be readily traced, under the low-power 

 objective, because of this persistence in the nerve sheath of its normal comple- 

 ment of small, spindle-shaped mast cells. 



By day five no mast cells are visible in the mesentery, such granular cells 

 as are seen being macrophages containing basophilic debris. The vascular 

 network is again very obvious, thanks to the adventitial proliferation. In the 

 omentum, similar adventitial changes are present. The small cells forming 

 the centres of the milk spots are deeply stained: in and around the milk spots, 

 macrophages are numerous but there are no mast cells. Similarly, there are 

 no identifiable mast cells in the ear or in the subcutaneous connective tissue. 



100 



