162 



mouse and guinea pig expire when about three- 

 fourths of this gas have disappeared. Dr Priestley 

 observed, that if a mouse can stand the first shock 

 of being put into impure air, or has been habituated 

 to it by degrees, he will live a considerable time in 

 air in which other mice will instantaneously die *. 

 The following case, related by the late Dr Percival, 

 seems to prove that a similar observation may be ex- 

 tended to the human subject. An unfortunate man 

 descended into a coal-pit 9O feet in depth, soon af- 

 ter which the sides of the pit fell in. No assistance 

 could be rendered him till the afternoon of the se- 

 venth day, at which time he was found sensible and 

 spoke to his companions : his hands and feet were 

 extremely cold, and no pulse could be felt at the 

 wrist : he slept when not aroused to take nourish- 

 ment, and lived a few hours after being taken out 

 of the pit. The compass of the cavity which he had 

 dug, and in which he was laid on his belly when his 

 companions reached him, was three yards in length 

 and two in breadth, and the stratum of coal was two 

 feet thick* No circulation of air could possibly 

 have taken place through this cavity ; and the foul- 

 ness of the vapours which issued from it, prevented 

 any one; for some time, from venturing to his assist- 

 ance f. Now, the capacity of a cavity, nine feet 

 long, by six wide and two deep, will be equal 

 to 108 cubic feet ; from which, if we deduct three 

 feet, as the space occupied by his body, the actual 



* Experiments on Air abridged, vol. iii. p. 257. 

 f Manchester Memoirs, vol. ii. p. 467. 



