Sect. II.] Physiology. 289 



brought by means of caloric to the state of elastic 

 fluids. In the following year that eminent philo- 

 sopher discovered that a quantity of carbonic acid 

 gas is found in air after it has been respired for 

 some time, which did not previously exist in it. 

 Some time afterwards he found, by a variety of ex- 

 periments, that no animal can live in air totally 

 deprived of oxygen. This fact was soon confirmed 

 and extended by the experiments of many other 

 philosophers, who proved that even fishes, which 

 do not perceptibly respire, and frogs, which can 

 suspend their respiration at pleasure, speedily die 

 if the water in which they are placed become 

 destitute of oxygenous gas*. 



By a further prosecution of observations and 

 experiments on this subject, it was not long after- 

 ivards satisfactorily establislicd, that certain re- 

 markable changes are produced by respiration not 

 only upon the air respired, but likewise upon the 

 blood exposed to this air. The most noted changes 

 observed to take place, in the air itself subjected to 

 respiration, are the following :— a part of the air 

 respired entirely disappears ; the rest becomes im- 

 pregnated with carbonic acid, and is loaded with 

 Water in the state of vapour. For the knowledge 

 of these changes effected in the air respired, and for 

 the numerous and laborious experiments from which 

 these conclusions were inferred, the world is chiclly 

 indebted to Priestley, Cigna, Lavoisier, MenzitSj 

 Seguin, and Davy. 



Changes no less remarkable are found to be 

 produced in the blood exposed to the air in the 



* Carradori^ Ann. dc Chim. xxi\, i;i. 

 Vol. I. U 



