THE MAST CELLS 



abortive or degenerating metachromatic eosinophils'. Thus in Jordan's view 

 (p. 103) 'metachromaticity of staining reaction is a phase of the ripening 

 process of the eosinophil granule. This is a novel conception of the meta- 

 chromatic granule, as distinct from the orthobasic granule, but the evidence 

 seems to permit of no escape.' 



Novel as this conception may be, it must be conceded that there are few who 

 would agree with Jordan that metachromatism in the granules of connective 

 tissue cells implies either that the cells are degenerating eosinophils or that 

 they are eosinophils which are ripening so slowly that they will now never 

 achieve maturity. A mere glance at a suitably stained tissue spread from many 

 higher animals is enough to shake such a belief. In rodents and cattle the 

 connective tissues are often packed with cells filled with basophilic or basophilic- 

 metachromatic granules, whereas eosinophils may be entirely lacking. Indeed, 

 it might be as plausibly argued from Jordan's data that it is the metachromatism 

 of the granules which signifies that the cell has reached full maturity and that 

 any subsequent eosinophilic staining is a sign of degeneration; certainly this 

 concept would be more in agreement with the findings of Kollmann (1908) 

 and Kindred (1926) on the 'amoebocytes with spherules' in invertebrates and 

 with the work of others who have subsequently examined the granular cells 

 in fishes (Romieu, 1924; Bolton, 1933; Duthie, 1939). However, there are 

 great difficulties in interpreting the histological appearances shown by the 

 granular cells in fishes, especially the cells in the wall of the gut. As Al-Hussaini 

 (1949, p. 334) remarks 'the picture is still further complicated by the fact that 

 the number of granules which are stainable by one technique may be quite 

 different from that seen with a different one, even in one and the same fish. . . . 

 This suggests that even in one species the granules may be of differing chemical 

 composition and hence may have several functions to perform.' Most modern 

 workers agree with Ehrlich (1878) that the mast cell is a cell 'sui generis', 

 generically and functionally different from the eosinophil. It is true that 

 eosinophils often occur along with mast cells in pathological conditions in 

 higher vertebrates but there may be another explanation for this. 



To sum up. Mast cells or their homologues are demonstrable in the tissues 

 of many invertebrates and lower vertebrates, and the sites at which these cells 

 are found in relation to the more general problem of blood formation suggests 

 an explanation for the presence of mast cells in marrow and tissues. The 

 gradual withdrawal of much of the original haemopoietic tissue into the bone 

 marrow, and the enclosure of the progenitors of the lymphocytes in nodes and 

 spleen, still leaves at the sites of former haemopoietic activity a scattered 

 residuum of what Maximo w (1924; 1926) has called 'undifferentiated mesen- 

 chymal cells'. One possible line of development of these cells is the tissue mast 

 cell. 



12 



