THE MAST CELLS 



rather the connective tissue habitat of the cell and the size and number of its 

 granules than the immediate staining qualities of the granules themselves: 

 'coarse granulocyte' is perhaps the more appropriate term for such cells. 

 With these considerations in mind we may first review in general terms the 

 evolutionary development of the mast cell in a series of organisms of increasing 

 complexity, and later examine in somewhat greater detail the distribution of 

 tissue mast cells in vertebrates. 



INVERTEBRATES 



It has been suggested that the metachromatic bodies in certain bacteria 

 and the volutin granules in yeasts (Guilliermond and Marvas, 1908; Wermel 

 and Sassuchin, 1927) correspond to mast cells in higher organisms; but in view 

 of the doubtful histo-chemical significance of metachromasia no great import- 

 ance can be attached to these claims (Tulasne and Vendrely, 1947; Duguid 

 et al, 1954). Nevertheless, in such lowly multicellular organisms as sponges 

 (Cotte, 1904) and simple coelenterates (Kollmann, 1908) well-defined basophilic 

 granular cells are already present in the connective tissues from which, in some 

 species, they escape as free cells into the primitive body cavity. Both Cotte 

 (p. 547) and Kollmann (p. 213) are of the opinion that these cells correspond 

 to the mast cells in higher forms. Such 'amoebocytes with spherules' are 

 common in echinoderms, especially in the walls of the ambulacratory pockets 

 of the star fish and sea urchin (Kollmann, 1908; Kindred, 1926) from which 

 a yellowish substance can be extracted from the granules by transferring the 

 organisms to tap water (Pequegnat, 1948). According to Kindred (1926) the 

 'coarse granulocyte' in echinoderms is first recognizable as a connective tissue 

 cell with clear cytoplasm, and thus corresponds to the 'hyaline cell' of Kollmann 

 (1908). Under conditions of good feeding the cell develops bulky refractile 

 spherules which stain with basic dyes. The spherules then progressively become 

 yellow and shrunken; finally often red and acidophilic. Thus the intermediate 

 coarse granulocyte in invertebrates, the cell with colourless, basophilic spherules, 

 bears the most obvious resemblance to the mast cell of higher animals. Kollmann 

 found these cells in the connective tissues of various invertebrate forms which 

 he examined. 'Les cellules spheruleuses . . . restent habituellement cantonnees 

 dans le tissu conjonctif. On peut vraisemblement les comparer aux Mastzellen 

 des Vertebres' (Kollmann, p. 200). Thus it will be observed from the stand- 

 point of comparative morphology that mast cells are regularly demonstrable 

 before the demand for oxygen and nutriment has led to the evolution of a 

 definitive blood-vascular system. Whatever may be the function of the mast 

 cells in these simple organisms it can hardly be concerned with the blood. 



The common blood cell of many insects appears to be concerned function- 



