fn a similar quantity of common air, another animal 
lived seven minutes; and Dr Priestley concluded , 
" that the restored air wanted about one-fourth of 
being as wholesome as common air *." In another 
experiment, a fresh mouse lived 14 minutes in two 
and a half ounce measures of respired air, that had 
been restored by vegetation ; and in air, rendered in- 
capable of supporting the flame of a candle by Dr 
Priestley's own respiration, he also found, that a can- 
dle would again burn, after a sprig of mint had been 
made to grow in it. In this case too, the effect, he 
adds, was not owing to any virtue in the leaves, but 
to the vegetating powers of the plant f. 
249. In these experiments, the same sources of 
fallacy may be pointed out as in those made on air 
injured by combustion* No precaution was taken 
to remove the carbonic acid formed by the respira- 
tory process, nor is it stated whether the experiments 
were conducted in sunshine, or in the shade. The 
higher orders of animals, also, die in confined gas 
some time before the whole of the oxygen is consum- 
ed, so that vegetation might, to a certain extent, go 
on in air incapable of supporting animal life. 
250. Dr Priestley, in the last place, endeavoured 
to restore the purity of air that had been injured by 
the putrefaction of vegetable and animal bodies^ 
His general hypothesis required that vegetables- 
should continue to live, and that animals should die y 
in such vitiated air ; but he observes that insects, o 
* Obs. on Air, abridged, vol. iii. p. 266. 7. 
f Ibid. p. 26S, 
