[ i8a ] 



it has ever been. I flatter myfelf, however, that I 

 have hit upon two of the methods employed by 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 vita, 

 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 affected 

 fo faddenly, that they are irrecoverable after a fingle 

 infpiration, though they be withdrawn immediately, 

 and every method has been taken to bring them to life 

 again. They are affected 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 brimitone, infected 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 ffand the firft fhock of this flimulus, 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 actually lived in it, a frefh moufe has been 

 inftantly thrown into convulfions, and died upon 

 being put to therru It is evident, therefore, that if 



the 



