THE MAST CELLS 



into larger metachromatic cells in the nearby connective tissue. His Figure 8 

 (p. 65) shows a tissue spread from a rat in which the majority of the cells are 

 disposed, as I have described them, outside the muscle coat of a small arteriole. 

 Both Waldeyer (1875, Fig. 1) and Ehrlich (1877, Fig. 8) depict a similar 

 arrangement of mast cells in the adventitia of blood vessels: yet Ehrlich 

 believed the mast cells to be concerned with the nutrition of the connective 

 tissue. Thus very similar illustrations have been submitted in the past in 

 support of two entirely different functions of the tissue mast cells. 



So far as the present investigation is concerned, the evidence both from cattle 

 and rats indicates that although mast cells are very common around small 

 blood vessels, their number is determined more by the extent to which such 

 vessels are equipped with an adventitial coat of mesenchymal cells than with 

 a functional relationship between the mast cells and the contents of the vessels. 

 One layer or more of muscle usually separates the mast cells from the lumen, 

 and, as the cells mature, they tend to move even farther away from the vessels 

 into the tissues. This is well seen in the rat. The available evidence thus 

 suggests that the presence of mast cells in the adventitia of small blood vessels 

 is, in fact, no different from their presence around the great veins and arteries, 

 and that this is merely an extension of conditions which obtain in the subserous 

 connective tissue of the nearby pericardium. Pericardium, in turn, resembles 

 pleura, or liver capsule, or peritoneum, all of which are rich in mast cells. 

 This is best seen in cattle. Similar loose connective tissue contributes to the 

 formation of the capsules and trabeculae of organs anatomically remote from 

 the serous membranes: it occurs in the submucosa of the gut and fills the chinks 

 between the bundles of voluntary muscles. Such tissue underlies the synovia 

 of joints and can be found also in the joint capsule. It underlies surface 

 epithelium, especially where that epithelium can be moved freely over the 

 corium; it is, in fact, the cause of that mobility. In short, the common de- 

 nominator which determines the presence of mast cells in an organ is the extent 

 to which that organ contains loose, well-vascularized connective tissue. Hence 

 it seems very probable that the mast cell is itself related functionally to the 

 connective tissues, and more especially to connective tissue at one particular 

 stage of its development, the stage of fibrillogenesis (Staemmler, 1921). 



58 



