99 



83. When atmospheric air is respired by man and 

 by other animals, it undergoes two remarkable chan- 

 ges : its bulk is diminished, and its qualities are altered. 

 This diminution of bulk was early noticed by Boyle, 

 who estimated it at about of the air employed. 

 May how, whose genius enabled him to anticipate so 

 many important discoveries of modern chemistry, 

 confined an animal in a glass-vessel inverted over 

 water, and, by the aid of a syphon, brought the 

 water on the inside of the vessel to a level with that 

 on its outside. Having then marked the height of 

 the water by pieces of paper affixed to the vessel, he 

 observed its gradual rise as the animal continued to 

 breathe : and then comparing the space occupied by 

 the air at the commencement of the experiment, 

 with that which it possessed when the animal ceased 

 to breathe, he found that it was reduced about j^ 

 part of its bulk *. In the experiments of Dr Hales, 

 the degree of diminution varied from ~ to ~- of the 

 whole air employed f : and in those of M. Lavoisier 

 from i to ij part J ; with which the results of Dr 

 Goodwyn's experiments on his own respiration nearly 

 coincide ||. Dr Priestley confined a mouse in a jar 

 containing a given quantity of air, which was invert- 

 ed over mercury : the animal \vas suffered to remain 

 two or three days after he had died, in which time 

 there was no sensible diminution of the air, but 



* Tractat. Ouinq. p. 104. 



f Statical Essays, vol. i. p. 238 vol. ii. p. 320. 



t Mero.-Acad. 1777 and 1780. 



[! Connexion of Life with Respiration, p. 51. 



G2 



