MAST CELLS IN HISTAMINE AND SKIN 



high — cat, mouse, and rat. The histological appearances in these three species 

 are shown in Figures 57, 58 and 59 which are all of the same magnification; 

 the arrows indicate the level at which the dermis can be scraped off. When the 

 histological appearances are compared with the values for histamine in Table 

 XXV we see that the mouse, with the highest total skin histamine, has two 

 layers of mast cells and two concentrations of histamine — one in the inner and 

 a second in the outer zone of skin. The cat and rat each have only one main 





M^ ^g 



?&&Z9F 



-■<-- 



^ : . . .. • V, > • -.;&• 



Fig. 59 



Rat skin. Staining and magnification as in Figs. 57 and 58. Here 



the mast cells lie mainly below the arrows and are removed, along 



with most of the histamine, when the dermis is scraped off. Contrast 



cat skin. Fig. 57. 



concentration of mast cells and histamine; yet the two species differ in that the 

 mast cells and histamine in the cat's skin are chiefly in the outer layer, close to 

 the epidermis, whereas the mast cells and histamine in the rat are mainly in 

 the inner layer, which can be removed by the technique described above. Not 

 only do the various histamine values for the two layers reflect the number of 

 mast cells in each; they also reflect to some extent the size of the cells comprising 

 the layer. Thus it will be seen from Figures 57, 58 and 59 that the subepidermal 

 mast cells in cat skin, though numerous, are small compared with the mast 

 cells in the mouse and rat, and that the mast cells in the superficial layer in the 



149 



