THE MAST CELLS 



skin of the rat are themselves smaller than the more deeply situated cells. It is 

 curious that the smallest animal, the mouse, has the biggest mast cells and a 

 double layer of them in its skin. Simple enumeration of the mast cells fails to 

 record these qualitative differences. 



Table XXV 

 Comparison of mast-cell contents and histamine values in the outer and inner zones of various species 



= outer zone; I inner zone. When the mast-cell count is high, the standard deviation is also 

 given. The cells in the guinea pig are very small, and in the rabbit are so few that no accurate 

 figure can be supplied. In the remaining species there is a close correlation between the number 

 and size of the mast cells and the local concentration of tissue histamine. 



Histamine and mast-cell profiles in the skin of the cat 



The success which attended the above procedure of splitting skin into an 

 inner and an outer layer suggested that it might be worthwhile to attempt a 

 more thorough division of skin from various species into several layers, using 

 the 'histamine profile ' method of Feldberg and Harris (1953) and combining 

 it with a histological assessment of the mast cells at the various levels. Com- 

 paratively thick skin is required for this purpose. Data for dog skin have 

 recently been submitted by Graham and associates (1955), hence, by way of 

 illustration, only the results with cat skin are recorded here. 



Materials and methods. Freshly excised abdominal skin of the cat was 

 clipped short, and portions of suitable size were placed on the freezing microtome 

 and sliced, parallel to the surface, at an average thickness of 40 \i. Alternate 

 slices were either weighed separately and extracted for histamine, or were 

 stained as frozen sections with toluidine blue and examined for mast cells. 

 A further sample of the original specimen was fixed and embedded for paraffin 

 sections. These were cut vertical to the surface in the conventional manner and 

 were stained by the methods previously described. 



Results. There was no doubt as to the relative location of the mast cells 

 in the frozen sections, though many of the cells displayed the dissolution of 

 granules and diffusion of metachromatic material which follow the use of a 

 watery technique (Michels, 1938). By far the greater number of mast cells 

 were encountered in the first three slices below the epidermis, in which situation 

 small granular mast cells of normal appearance were seen in the paraffin 



150 



