COMPOUND 48/80 ON RAT 



Recovery is slowest in the mesentery, which, by day eight, contains only 45 per 

 cent of its initial histamine. By day fifteen all the above-mentioned regions 

 have achieved an 80 per cent recovery or better, and by day thirty-two, the 

 restoration of tissue histamine is complete. 



'Subacute dosage' experiment 



In this group, injected intraperitoneally twice daily for five days with a 

 steadily increasing level of dosage, the animals rapidly acquired tolerance and 

 by the fifth day showed little evidence of histamine release following injection. 



*& 



* 





tor 3 



Fig. 34 



' Subacute dosage ' experiment. Subcutaneous connective tissue on third day of intra- 

 peritoneal injection of the histamine-liberator. One exceptionally large mast cell near 

 the top remains unaffected. The remaining mast cells, in a slightly different tissue plane, 

 all show varying stages of swelling and degranulation — ' ghost ' cells. This is a reversible 

 process. Toluidine blue ( x 350). (Riley and West (1955), J. Path. Bact. 69, 269.) 



* I 



Mast cells. Histological examination began on day three, by which time 

 the mast cells in regions remote from the injection site already show changes 

 far exceeding anything observed in the 'acute dosage' experiment. There is 

 an absolute decrease in the number of mast cells in the subcutaneous connective 

 tissue and in the skin of the ears. Such cells as remain are recognizable only 

 by the presence of a few clumped granules or of small pale granules situated at 

 the periphery of greatly swollen cells ('ghost' cells). These 'ghost' cells are 

 well seen in the interspaces of the subcutaneous connective tissue (Fig. 34), the 



99 



