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in that part of the air, in which the fprig of mint had 
grown, but died the moment it was put into the 
other part of the fame original quantity of air; and 
which I had kept in the very fame expofure, but 
without any plant growing in it. 
This experiment I have feveral times repeated ; 
fometimes uling air, in which animals had breathed 
and died ; fometimes ufing air tainted with vege- 
table or animal putrefadion, and generally with 
the fame fuccefs. 
Once, I let a moufe live and die in a quantity of 
air, which had been noxious, but which had been 
reftored by this procefs, and it lived nearly as long 
as I conjedured it might have done in an equal quan- 
tity of frefh air ; but, this is fo exceedingly various, 
that it is not eafy to form any judgment from it ; 
and in this cafe the fymptom of difficult refpiralion 
feemed to begin earlier than it would have done in 
common air. 
Since the plants that I made ufe of manifeftly 
grow and thrive in putrid air; fince putrid matter 
is well known to afford proper nourifhment for the 
roots of plants ; and fince it is likewife certain that 
they receive nourifhment by their leaves as well as 
by their roots, it feems to be exceedingly probable, 
that the putrid effluvium is in fome meafure extrad- 
ed from the air, by means of the leaves of plants, and 
therefore that they render the remainder more fit for 
refpiration. 
Towards the end of the year fome experiments 
of this kind did not anfwer fo well as they had done 
before, and I had infiances of the relapfing of this 
reftored air to its former noxious ftate. I therefore 
fufpended 
