THE MAST CELLS 



association with a special type of loose connective tissue of wide distribution 

 than with any particular organ. Due weight must be accorded to this fact in 

 any hypothesis which attempts to explain the function of the mast cell. 



MAST CELLS IN THE RAT: THEIR RELATIONSHIP TO 

 THE BLOOD VESSELS 



(See Riley, 1953a) 



Examination of mast cells in tissue spreads of subcutaneous connective 

 tissue and peritoneum from cattle was often rendered difficult by the presence 

 of fat, which continued to escape from intact fat loculi in the mounted prepara- 

 tions despite their having been previously immersed in xylol for as long as 

 forty-eight hours. This was the more troublesome as one of the objects of the 

 present study was to determine the precise relationship of the mast cells to the 

 small blood vessels which are otherwise admirably displayed in preparations 

 of this kind. Accordingly, a number of the common laboratory animals were 

 examined with a view to finding one from which permanent tissue spreads 

 could be made and upon which, if necessary, various experimental procedures 

 could be carried out. Of the species examined (dog, cat, guinea pig, rabbit, 

 hamster, mouse) the Wistar strain of albino rat appeared to be the most 

 suitable. A preliminary survey of its tissue mast cells was therefore first 

 undertaken, as in the previous survey of the tissue mast cells in cattle. 



The following tissues were examined. Sections of brain, lung, thymus, 

 oesophagus, stomach, duodenum, large and small intestine, spleen, pancreas, 

 liver, kidney, uterus, skin and muscle. Tissue spreads of dura mater, sub- 

 cutaneous connective tissue, dorsal skin and subcutis of ear, diaphragm, 

 mesentery, omentum and the peritoneal fringes which are attached to uterine 

 horns in female rats (Figs. 11-18). 



Results. Again the most striking single finding arising from this survey of 

 mast cells in the rat is the astonishing abundance of mast cells in the connective 

 tissues and serous membranes in contrast to the paucity of mast cells in the 

 parenchymatous organs. There are no mast cells in the brain substance or 

 in the kidney, and very few in the liver, spleen and pancreas (Fig. 16) though 

 they are found in the meningeal or peritoneal coverings of these organs.* 

 Mast cells are rare even in the lung. The comparatively small numbers which 

 are seen in the thymus are situated almost exclusively in the loose peri-thymic 

 and inter-lobar connective tissue. A few occur also in similar connective 

 tissue in the diaphragm and in the loose connective tissue lying between the 



* It is interesting now to consult the original article by Waldeyer (1875) and observe his excellent 

 illustration (Fig. 1, pi. IX) of the so-called ' plasma cells ' near blood vessels in a tissue spread of 

 rat dura mater. These are obviously tissue mast cells. 



48 



