MAST CELL IN EVOLUTION 



Relationship of mast cells to eosinophils. Before leaving the subject 

 of the mast cells in the lower vertebrates we may briefly consider the views of 

 Jordan and his school on the relationship of mast cells to eosinophils in blood 

 and tissues. This is particularly necessary since Jordan's conclusions at first 

 appear to be in conflict with those of most other workers in this field. 



In his earlier studies on blood formation in reptiles (Jordan and Flippin, 

 1913) and amphibia (Jordan, 1919) Jordan adopted a conventional outlook 

 and regarded the mast cell as a specific variety of granulocyte distinct from 

 and genetically unrelated to the eosinophil. The distinction is clear, even in 

 many arthropods: in certain crayfish, for example, eosinophils stem from a 

 highly localized tissue ('orgagne globuligene' of Cuenot, 1905) whereas, as we 

 have seen, the metachromatic basophils in the crayfish are of widespread 

 perivascular origin (Hardy, 1892). Later, however, Jordan and Speidel (1924a) 

 failed to find basophils in certain fish but were impressed by the abundance of 

 irregular amoeboid eosinophils in the gut wall of the teleostean scup and tautog. 

 Similar conditions apparently obtained in a reptile, the terrestrial salamander 

 (Jordan and Speidel, 1924/?). On reviewing their data in the light of an earlier 

 study of blood formation in the frog (Jordan and Speidel, 1923), these authors 

 conclude that the eosinophils arise from lymphocytes or undifferentiated 

 connective tissue cells and that the remaining cells with basophilic granules 

 are either 'unripe eosinophils 1 or, if the granules are bulky, irregular and 

 metachromatic 'eosinophils in course of degeneration'. According to Jordan 

 and Speidel (1923) such 'abortive eosinophils' are common in the spleen of 

 the bullfrog. Meanwhile Michels (1922; 1923) had studied the dense accumula- 

 tions of granular cells in the tissues of many lower vertebrates and had concluded 

 that morphologically and from their connective tissue habitat such cells are to 

 be regarded as mast cells. Nevertheless, Jordan (1926, p. 99) insists that 'the 

 granulocytes described and illustrated by Michels in various fish tissues, 

 stained metachromatically red with thionin and interpreted by him as mast 

 cells, are apparently strictly homologous with very similar cells occurring in 

 the gut wall of the scup and tautog (Jordan and Speidel, 1924a) where they are 

 definitely oxyphilic; and with those in the intestines of the leopard frog where 

 they are distinctly metachromatically basophilic. They are apparently identical 

 also with the tissue eosinophils which differentiate in the connective tissue of 

 the intestinal submucosa, and with the eosinophilic and special granulocytes 

 which develop in large part from the reticular cells in the peripheral area of the 

 femoral marrow of the rabbit; and with comparable cells with a similar origin 

 in the subcapsular region of the liver of the salamander, and in the capsule and 

 septa of the ovaries and testes of the skate' .... Apparently, then, he goes on 

 (p. 104), 'the so-called mast cells include three varieties: initial orthobasic 

 granular progenitors of eosinophils, ripening metachromatic eosinophils, and 



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