IXXU INTRODUCTORY OBSERVATIONS, 



air, or where the circulation is impeded, will be 

 deftroyed ; and that plants in fuch a fituation 

 will droop and die. — Late refearches in chemiftry 

 have difcovered various invifible fluids produc- 

 ed by different fubftances, which are fatal to the 

 animals that refpire them. Some are fo deftruc- 

 tive as to occafion inflant diffolution ; in others, 

 an animal may linger long, though it will at laft 

 perifli under their deleterious influence. Nay, 

 eminent philofophers have fallen a vidim to ha- 

 zardous experiment on themfelves : and feveral 

 have efcaped after the moll imminent danger. 



I So ufeful is atmofpherical air to the conferva- 

 tion of life, and fo dependent is life on its influ- 

 ence, that none of the animals, with whofe na- 

 ture we are acquainted, can exifl without it 

 entirely : and if fome do fupport privation of air 

 better than others, ftill they languifh, and at 

 length will die. Thofe inhabiting waters, and 

 feldom come to the furface for refpiration, perifli 

 when the water is deprived of the pure air which 

 it contains. 



Atmofpherical air is not a fimple fluid ; it is a 

 combination of various fluids ; fome of which, in 

 a decompofed and feparate fl:ate, are better calcu- 

 lated to fupport life, at leaft; for a certain timCj, 

 than the refl:, but none except itfelf has yet been 



found 



