THE MAST CELLS 



of rats is a hyperplasia of the adventitial tissue and milk spots, without, however, 

 any reappearance of typical mast cells. Occasional granular cells are seen but 

 they are very rare. In the control group of rats, the mast-cell picture is normal, 

 apart from an occasional pale or 'punctate' mast cell in the mesenteric windows 

 and a few additional polymorph leucocytes in the omentum. If anything, 



• EARS 



SUBCUTI S 



DAYS 



Fig. 39 



' Chronic dosage ' experiment. Effect of 48/80, given over thirty-one days, on 



histamine content of subcutaneous connective tissue (O O) and ears 



(• •) of rats. Histamine content expressed in /xg./g. tissue in the upper 



tracings and in percentage of normal values in the lower tracings. Note the 

 partial recovery in the histamine content of the subcutaneous connective tissue, 

 despite the continued dosage of 48'80. (Riley and West (1955), ./. Path. Bact. 



69, 269.) 



there is an increase rather than a decrease in the number of omental mast cells 

 in the saline-treated controls. 



As the experiment proceeds an interesting difference emerges between the 

 appearance of the mast cells in the two remote tissues, ears and subcutaneous 

 tissue. Mast cells progressively disappear from the ears (with the exception of 

 the nerve sheaths) and remain absent thereafter. In the subcutaneous connec- 

 tive tissue, on the other hand, the inital disappearance of the cells is followed by 

 the gradual development of numerous minute mast cells in the adventitia of 



104 



