[ i8j 3 
it has ever been. I flatter myfelf, however, that I 
have hit upon two of the methods employed bv na- 
ture for this great purpofe. How many others there 
may be, I cannot tell. 
When animals die upon being put into air 
in which other animals have died, after breathing in 
it as long as they could, it is plain that the caufe of 
their death is not the want of any pabulum vitce^ 
which has been fuppofed to be contained in the air, 
but on account of the air being impregnated with 
fomething ftimulating to their lungs ; for they almoft 
always die in convulfions, and are fometimes affedted 
fo fuddenly, that they are irrecoverable after a Angle 
infpiration, though they be withdrawn immediately, 
and every method has been taken to bring them to life 
again. They are affedted in the fame manner, when 
they are killed in any other kind of noxious air that 
I have tried, viz. fixed air, inflammable air, air 
filled with the fumes of brimftone, infedted with 
putrid matter, in which a mixture of iron filings and 
brimftone has flood, or in which charcoal has been 
burned, or metals calcined, or in nitrous air, &c. 
If a moufe (which is an animal that I have com- 
monly made ufe of for the purpofe of thefe experi- 
ments) can ftand the firft fhock of this ftimulus, or 
has been habituated to it by degrees, it will live a 
confiderable time in air in which other mice will 
die inftantaneoufly. I have frequently found that 
when a number of mice have been confined in a 
given quantity of air, lefs than half the time that 
they have adtually lived in it, a frefh moufe has been 
inftantly thrown into convulfions, and died upon 
being put to them. It is evident, therefore, that if 
