HISTAMINE-LIBERATION IN MOUSE AND RAT 



small, darkly staining cells. These changes are again reflected in the histamine 

 values (Table XVI and Fig. 42), the initial depletion in the subcutaneous 

 connective tissues (to 6 per cent of normal) being followed by a recovery to 

 about 60 per cent of normal. 



Table XVI 



Histamine content of tissues of rats following 



treatment with 48/80 over 31 days (Long-term 



experiment ) 



Values expressed in \xg. g. tissue 



Long-term experiment in mice. Continued dosage brings out a significant 

 difference between the rat and the mouse in response to injections of a histamine- 

 liberator. The initial decrease in the histamine content of the tissues (to 50 

 per cent of normal) seen in both species is not progressively continued in the 

 mouse despite the relatively large daily doses of the liberator (Table XVII and 

 Fig. 42). By day thirty-two, groups of mast cells are still present in the ears and 

 subcutaneous connective tissue of mice. They appear to be resistant to these 

 doses of the liberator, which are the maximum tolerated. 



Table XVII 



Histamine content of tissues of mice following 



treatment with 48 80 over 31 days (Long-term 



experiment) 



Values expressed in [ig./g. tissue 



Discussion 



The above experiments indicate that the same chemical substance, com- 

 pound 48/80, acts differently on two closely allied species, the mouse and rat. 



H 



113 



