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thefe infects which infected them $ ai;d yet fo ef- 

 fectually did ibme of them conceal themfelves, and 

 fo faft did they multiply, in thefe circumstances, 

 that I could feldom keep the plants quite clear of 

 them* 



When air has been frefhly and ftrongly tainted 

 with putrefaction, 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; frem moots 

 have branched out in various directions, and have 

 grown much farter than other limilar plants, grow- 

 ing in the fame expofure in common air. 



This obfervation led me to conclude, that plants, 

 inftead of affecting the air in the fame manner with 

 animal refpiration, reverfe the effects of breathing, 

 and tend to keep the atmofphere fweet and whoie- 

 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, Itook 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, ftand- 

 ing in water) I put a fprig of mint. This was about 

 the beginning of Augufr. 1771, and after eight or 

 nine days, I found that a moufe lived perfectly well 



Vol. LXIL C c ia 



