THE MAST CELLS 



parallelism between the histamine values and mast-cell contents of the various 

 topographical regions of the ear. Thus, there is more histamine in the upper 

 than in the lower skin, and more at the tip than at the base. The central 

 cartilage, though displaying as strong a metachromatism as the mast granules, 

 contains little histamine, and even this may perhaps be due to the few mast cells 

 in the perichondrium. A high content of mast cells has been previously noted 



Fig. 56 



Whole mount, upper skin mouse ear. Fixed alcohol, stained toluidine blue ( 64). Enormous 



numbers of mast cells are present; many of them surround the hair follicles. The skin of the 



ear contains proportionately more histamine than any other tissue. 



in the ears of mice and rats (Figs. 18 and 56). However, the ears of these 

 smaller animals are less suited to a regional survey of mast cells and histamine 

 than are the ears of larger animals. Only the upper skin of the ear of the mouse 

 and rat can readily be stripped off the cartilage, though it has the advantage 

 of being so thin that it can be examined histologically as a whole-mount 

 preparation (Fig. 56). This upper skin in mouse and rat contains about three 

 times as much histamine as the remainder of the ear, cartilage and lower skin 

 together. 



Thus, these preliminary findings using the ears of various species support 

 the idea that there is a close association between the histamine content of a 



146 



