of Cancer , and on Animal Hepatic Air „ 423 
The peculiar fmell of animal hepatic air is likewife de- 
ft royed by agitating it with vinegar, or with the concentrated 
vitriolic acid. But the fluids which moft fpeedily produce this 
effedt, are the concentrated nitrous and dephlogifticated marine 
acids; and thefe fluids are known to abound with pure air. It is 
therefore extremely probable, that this alteration depends upon 
an union between the pure air of the latter fubftances and the 
animal hepatic air, or fome of its conftituent parts. 
It appears from the experiments which have been recited 
above, that in cancerous and other malignant ulcers, the ani- 
mal fibres undergo nearly the fame changes which are produced 
in them by putrefadtion, or by deftrudtive diftillation. The 
purulent matter prepared for the purpofe of healing the ulcer 
is, in fuch cafes, mixed with animal hepatic air and volatile 
alkali. The compound formed by the union of thefe fub- 
ftances, which may perhaps not improperly be termed hepa- 
tifed ammonia, decompofes metallic falts, and adts upon me- 
tals : for we have feen, that when it was placed in ajar over 
mercury for feveral days, the fur face of the mercury acquired 
a black colour ; and that it inftantly occafioned a dark precipi- 
tate in a folution of nitrated filver. Thefe fadls feem to afford 
an explanation of the changes produced in metallic falts, when 
they are applied to malignant ulcers. The volatile alkali com- 
bines with the acid of the metallic fait, and the animal hepa- 
tic air revives the metal, either by imparting to it the inflam- 
mable principle, or by uniting with the pure air which the 
calx is fuppofed to contain. The metal, thus revived, is pro- 
bably in fome cafes again corroded by the hepatifed ammonia, 
which communicates to it a black colour. Thus we may 
account for the dark ingruftation frequently formed upon the 
tongue 
