C 59 ] 
much as when a perfon has his mouth near a large 
tube of a hot brafier, or when he goes into a very 
hot and moifl dove. I alfo felt a flight acrimony in 
the throat and nofe, which made me cough and 
fneeze. But this trial, which I mull own was of 
fhort duration, occafioned neither ficknefs at domach, 
nor head -ach, nor any other inconveniency. It con- 
firmed me more than ever in the opinion, that this 
vapour had none of thofe venomous or pedilential 
qualities, which are attributed to mof eta's , tho’ it is 
claffed among them by feveral authors. 
For my part, when I conlider the quicknefs of its 
action, I fee nothing in it but a fluid, the nature of 
which is indeed unknown to me, but which is fpe- 
cifically heavier than the air, and does not eafily mix 
with it. And this I take to be fufficient to account 
for the effects, that are obferved in the grotto. 
It is well known, that the air is, for land-animals, the 
only proper fluid for refpiration ; and for this purpofe it 
mud have a certain degree of purity and denfity. A 
quadruped or a bird would foon perifh for want of 
breath in the beft and mod wholfome water ; and 
nobody could live long in a very thick fmoke, tho' 
it were that of burnt draw, or any other more in- 
nocent matter ; he would foon be fmother’d in it. 
The fame thing may be faid with regard to flame ; 
it extinguishes necefiarily, when it is deprived of air ; 
no other medium fuits it. Now, of what nature fo- 
ever the vapour of the grotto may be, from the 
moment we are certain, that it is not air, or that it 
is not an air like that of the atmofphere, it is eafy to 
fee, why animals cannot breathe it. They perifli in it, 
not as poifoned, but barely are drowned in a fluid in-’ 
capable of fupplying the place of the air, which they 
H 2 want: 
