THE MAST CELLS 



tissue, and the clue may lie in the distribution of the metachromatic material. 

 The two types of metachromatism — the diffuse metachromatism of ground 

 substance and the compact granular metachromatism of mast cells — are present 

 alternately in the series of changes outlined above, suggesting that whatever 

 their chemical relationship may be they bear an inverse functional relation to 

 one another. The precursor of the metachromatic ground substance present 

 in the embryo would seem to stem from the connective-tissue cells themselves 

 and may undergo further elaboration in the tissue spaces (Schoenberg and 

 Moore, 1958). The major component of the ground substance is generally 



cooh o 



CH t OH 



o- 



NHOCCHj 



r\ 



HYALURONIC ACID 



COOH O CH.OH O 



l/H 

 \OH 



H 



H 



OH 



OH . . mucau 



+ 2SOH 



NHSO,H 



a 



HEPARIN 



Fig. 55 



Suggested formulae for heparin and hyaluronic acid. (Redrawn from Burkl, 

 1952.) (See Riley (1954), Lancet, p. 841, fig. 1.) 



believed to be hyaluronic acid. As cellular differentiation advances and the 

 ground substance shrinks, metachromatic mucopolysaccharides are seen to 

 concentrate as granules in the tissue mast cells. Yet this is more than a simple 

 phagocytosis of mucopolysaccharides by the mast cells. In addition to the 

 esterification of the molecule by sulphate, its internal structure is radically 

 changed. Indeed, complete hydrolytic breakdown of hyaluronic acid must first 

 occur before a re-synthesis to heparin is possible (Fig. 55). Yet in this way 

 the building blocks of a strongly hydrophilic colloid (hyaluronic acid) can be 

 stored in compact, dehydrated form (heparin), as foodstuffs were concentrated 

 and stored during the past war. Speculating thus, a hundred years after the 

 birth of Ehrlich, we come back to his original view of the mast cell as a 'well- 

 fed cell' of the connective tissue. 



Within recent years a number of workers have come to favour some form 

 of this general hypothesis relating the mast cell to the connective tissue. Sylven 



142 



