THE EARTH. 271 



tion it continued for twenty-three hours. But 

 upon the air's being re-admitted, the viper's 

 mouth was presently closed, and soon after open, 

 ed again : and for some time those motions con- 

 tinued, which argued the remains of life." Such 

 is the fate of the most insignificant or minute 

 reptile that can be thus included. Mites, fleas, 

 and even the little eels that are found swimming 

 in vinegar, die for want of air. Not only these, 

 but the eggs of these animals, will not produce 

 in vacuo, but require air to bring them to perfec- 

 tion. 



As in this manner air is necessary to their sub- 

 sistence, so also it must be of a proper kind, and 

 not impregnated with foreign mixtures. That 

 factitious air which is pumped from plants or 

 fluids, is generally, in a short time, fatal to them. 

 Mr Boyle has given us many experiments to this 

 purpose. After having shown that all vegetable, 

 and most mineral substances, properly prepared, 

 may afford air, by being placed in an exhausted 

 receiver ; and this in such quantities, that some 

 have thought it a new substance, made by the 

 alteration which the mineral plant has undergone 

 by the texture of its parts being loosened in the 

 operation having shown, I say, that this air may 

 be drawn in great quantities from vegetable, ani- 

 mal, or mineral substances, such as apples, cherries, 

 amber burnt, or hartshorn* he included a frog 

 in artificial air, produced from paste ; in seven 

 minutes space it suffered convulsions, and at last 



* Boyle's Physico-Mechan. vol. ii. p. 598. 

 56 



