THE MAST CELLS 



13. Finally, an enquiry is made into the mast-cell reaction in mouse skin 

 undergoing carcinogenesis from repeated surface applications of a polycyclic 

 hydrocarbon. Many of the mast cells under the painted skin show a golden- 

 brown fluorescence in ultra-violet light. This seems to be associated with a 

 high content of 5-hydroxytryptamine, a normal constituent of the mast cells 

 of the mouse and rat, though present in no other species. Work is in progress 

 to trace the sources of this high content of 5-hydroxytryptamine and to deter- 

 mine its significance. Now that something is known of the structure and com- 

 position of the normal mast cell it may be possible to arrive at an understanding 

 of the significance of the mastocytosis in precancerous mouse skin. It will be 

 recalled that it was for this reason that the present work was begun. 



164 



