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reeling the mafs of air contaminated 

 by their refpiration, and perhaps 

 too by their perfpiration. The fol- 

 lowing pages will ihew, whether 

 the pains I took, in the courfe of this 

 fummer, to inveftigate this impor- 

 tant fubjec~t,have been attended with 

 fome degree of fuccefs. I am far 

 from thinking that 1 have difco- 

 vered the whole of this falutary 

 operation of the vegetable kingdom ; 

 but I cannot but flatter myfelf, that 

 I have at leafl proceeded a ftep far- 

 ther than others, and opened a new 

 path for penetrating deeper into this 

 myfterious labyrinth. 



Among the various ufeful difco- 

 veries - w 7 ith which Dr. Prieftley has 

 already enriched, and ftill continues 

 to enrich, natural knowledge, none* 

 in my opinion,, are of more import- 

 ance- 



