THE MAST CELLS 



precursors in the adventitia of blood vessels, the septa of fat cells and the milk 

 spots and connective tissue framework of the omentum. On the other hand, 

 the mast cells in distant tissues reappear at once as large 'ghost' cells which 

 rapidly regain their basophilic granules. Since a few intermediate forms can 

 be found in all areas, we believe that these different sequences represent 

 the response to different doses of compound 48 80. Rather similar con- 

 clusions were drawn by Fawcett (1954), who studied the peritoneal mast 

 cells of rats after injecting graded doses of compound 48 80. It seems clear, 

 therefore, that although high dosage of a histamine-liberator kills mast cells 

 from which the histamine has been released, a more moderate dose effects a 

 reversible change, leaving the cells capable of recovery, as evidenced by 

 re-formation of stainable granules. It is probable that this reversible process 

 represents the normal mechanism of histamine release. 



Secondary effects of histamine release 



Among the incidental observations made in this work, the activation of 

 the loose mesenchyme which follows damage to the mast cells may prove to be 

 of physiological importance. It will be recalled that, as the mast cells disappear, 

 there is progressive swelling, basophilia and evidence of mobility of various 

 connective tissue cells, first of the adventitia itself and later of cells at increasing 

 distances from the blood vessels. Indeed, in such a tissue as the mesentery, 

 the histological picture soon comes to be dominated by the deeply stained and 

 swollen cells in the adventitia of the small blood vessels and by the appearance 

 of similar well-stained pleomorphic cells scattered over the peritoneal windows. 

 Some of these cells eventually become mast cells, some are evidently macro- 

 phages, but the majority appear ultimately to return to a state of quiescence 

 as the mast cells refill with granules. One wonders, therefore, whether this 

 temporary activation of the loose mesenchyme might not result from the flooding 

 of the tissues with a protein-rich oedema fluid consequent upon the release of 

 histamine (Drinker and Yoffey, 1941 ; Feldberg, 1954). If so, it might indicate 

 a physiological role for histamine in the inflammatory reaction. 



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