[ *93 3 
thefe infedls which infe&ed them ; and yet fo ef- 
fectually did fome of them conceal themfelves, and 
fo fall did they multiply, in thefe circumftances, 
that I could feldom keep the plants quite clear of 
them. 
When air has been frefhly and drongly tainted 
with putrefa&ion, fo as to fmell through the water, 
fprigs of mint have prefently died, upon being put 
into it, their leaves turning black ; but if they do 
not die prefently, they thrive in a mod furprizing 
manner. In no other circumftances have I ever 
feen vegetation fo vigorous as in this kind of air, 
which is immediately fatal to animal life. Though 
thefe plants have been crouded in jars filled with this 
air, every leaf has been full of life ; frelh (hoots 
have branched out in various directions, and have 
grown much fader than other fimilar plants, grow- 
ing in the fame expofure in common air. 
This obfervation led me to conclude, that plants, 
indead of affecting the air in the fame manner with 
animal refpi ration, reverfe the effeCts of breathing, 
and- tend to keep the atmofphere fweet and whole- 
fome, when it is become noxious, in confequence 
of animals living and breathing, or dying and pu» 
trefying in it. 
In order to afcertain this, I took a quantity of air, 
made thoroughly noxious, by mice breathing and 
dying in it, and divided it into two parts; one of 
which I put into a phial immerfed in water; and to 
the other (which was contained in a glafs jar, Hand- 
ing in water) I put a fprig of mint. This was about 
the beginning of Auguft 1771, and after eight or 
nine days, I found that a moufe lived perfectly well 
Vol. LXII. C c in 
