MAST CELLS AND HISTAMINE IN SKIN 



sections cut perpendicular to the surface of the skin. Two factors prevented 

 accurate counts being made of the mast cells in the frozen sections; first, the 

 actual thickness of the slices themselves (40 \l), and secondly, the loss of meta- 

 chromatic material, referred to above, which made it difficult to identify the 

 smaller mast cells. Accordingly, the requisite counts were made from the 

 paraffin sections (of which Fig. 57 is an example) by projecting a series of 



MAST CELL 



HISTAMINE 



PROFILE 



SLICE NO. 



1 



V77X 



HISTAMI NE 



H«j/<3 



MAST CELLS 



5 



PER TISSUE STRIP , » x SO* 2, COO fl 



I 2 3 4 5 6 7 B 9 IO II 12 13 14 15 16 17 18 19 20 21 



n(o 



■ 80>J- 



Sir 



I V 



Fig. 60 



Combined mast-cell and histamine ' profile ' of cat skin. Part of a drawing of a section, made 

 with the aid of a projection microscope, has been rotated to lie transversely across the diagram: 

 the broken lines indicate the levels at which alternate frozen sections were cut and assayed for hist- 

 amine. The histamine values are represented, along with the appropriate mast-cell counts, in the 

 upper half of the diagram. The two ' profiles ' show a striking resemblance to one another. 



microscope fields on to paper previously subdivided at that magnification into 

 strips 80 [x wide by means of a stage micrometer. Once the first line had been 

 adjusted to lie along the edge of the epidermis, the remaining pairs of lines 

 enclosed zones of tissue corresponding to those from which the histamine 

 samples had been taken in the frozen material. For convenience, mast cells 

 were counted in strips 2000 \i in length, i.e. in a block of tissue which, after 

 fixation and sectioning at 8 \x, occupies a volume of 8 X 80 x 2000 cu. \x. Cal- 

 culation then shows that in the region of maximal concentrations of mast cells 

 and histamine in the skin of the cat, each small mast cell contains approximately 

 1 -14 \i\ig. histamine. When the mast-cell counts and histamine values are plotted 



15! 



