1893.] The Gases in Living Plants. 3 
from his communication to the Royal Society, announcing the 
matter: 
“The quantity of air which even a small flame requires to 
keep it burning is prodigous. It is generally said that an 
ordinary candle consumes, as it is called, about a gallon in a 
minute. Considering this amazing consumption of air, by 
fires of all kinds, volcanoes, ete., it becomes a great object of 
philosophical inquiry, to ascertain what change is made in 
the constitution of the air by flame, and to discover what pro- 
vision there is in Nature for remedying the injury which the 
atmosphere receives by this means. 
“ I flatter myself that I have accidentally hit upon a method 
of restoring air which has been injured by the burning of 
candles, and that I have discovered at least one of the restora- 
tives which Nature employs for this purpose. It is vegetation. 
* * * One might have imagined that, since common air is 
necessary to vegetable as well as to animal life, both plants 
and animals had affected it in the same manner, and I own I 
had that expectation when I first put a sprig of mint in a 
glass jar standing inverted in a vessel of water; but when it 
had continued growing there for some months, I found that 
the air would neither extinguish a candle nor was it at all 
inconvenient to a mouse which I put into it. * * * Finding 
that candles burn very well in air in which plants had grown 
a long time, and having had some reason to think that there 
was something attending vegetation which restored air that 
had been injured by respiration, I thought it was possible that 
the same process might also restore the air that had been 
injured by the burning of candles. Accordingly, on August 
17, 1771, I put a sprig of mint into a quantity of air, in which 
a wax candle had burned out, and found that on August 27 
another candle burned perfectly well in it. This experiment 
I repeated, without the least variation in the event, not less 
than eight or ten times in the remainder of the summer.” 
Had Priestley had the good fortune to have set his jar con- 
taining green sprigs into direct sunlight, he would have made 
an additional discovery of almost equal importance. But the 
world did not wait long till Ingenhousz went over the ground 
