FUNCTION OF HEPARIN 



umbilical cord and described earlier (p. 15). If, however, the connective 

 tissue is later subjected to trauma — mechanical, chemical, thermal, bacterial — 

 whereby an 'acute watery oedema' is produced (Drennan, 1951), the mast 

 cells promptly release their metachromatic substance into the tissues (Sylven, 

 1941 ; and see Figs. 47 and 48). The appearance of tissues thus mobilized for 

 regeneration and repair closely resembles the histological conditions of embry- 

 onic connective tissue (Holmgren, 1939, 1940). Fibroplasia of shorter or 

 longer duration follows, and, as recognizable collagen begins to take its shape. 



Fibroblast 



Fibrils "**' 



Precursors 



r *« chromotrope 



Fig. 54 



The Mast-Cell Cycle. This illustrates the part played by the mast cell in the local 

 events of the connective tissues. Ground substance, derived originally from the fibro- 

 blast, is ultimately stored in altered, compact form in the mast cell: following 'trauma' 

 it can again be released and re-enter the cycle via mesenchymal cells whose main 

 source of fuel is the blood stream. 



mast cells once more appear in the reactive zone (Staemmler, 1921). Should 

 fibroplasia be unduly protracted, as in chronic inflammation, the mast-cell 

 population further increases (Janes and MacDonald, 1948); and in conditions 

 of chronic lymphatic obstruction, in which the tissue spaces remain loaded 

 with protein-rich oedema fluid, both connective tissue hyperplasia and mast- 

 cell hyperplasia become extreme (Baumer, 1896). The end-point is reached 

 with the formation of avascular scar tissue in which neither fibroblasts nor 

 mast cells are now present (Neumann, 1890). 



Such is the observed sequence; the difficulty lies in the interpretation. The 

 cyclic changes in the mast-cell population of loose connective tissue certainly 

 suggest that the mast cells are concerned in some way with the function of that 



141 



