156 



ring the continuance of the respiratory process, it is 

 next in order to examine how far the necessary dinv- 

 nution of bulk (123.) which attends that conversion, 

 will go to explain the absolute loss which the air, du- 

 ring its respiration, suffers. The amount of this loss 

 has been already stated to have been very variously- 

 estimated : and the cause of this variation in experi- 

 ments made on animals (83.) confined in jars of air, 

 has been explained. It is our present object to in- 

 quire into that degree of diminution which takes 

 place in air that has only once passed through the 

 lungs, and where all the circumstances of the expe- 

 riment resemble those which occur in the ordinary 

 process of respiration. Dr Goodwyn states, that 

 the volume of air, taken into the lungs at a single 

 inspiration, loses ~, or sometimes only ~ of its 

 bulk, when expelled from those organs by the next 

 succeeding expiration *. Dr Menzies, taking the a- 

 verage amount of the loss which the air suffered by 

 56 successive respirations, observes, that the volumes 

 of air, received into and expelled from the lungs, 

 were nearly the same t Several attempts were 

 made by Mr Davy to estimate the degree of diminu- 

 tion experienced by the air in a single respiration ; 

 and it has been shewn that his determinations great- 

 ly vary (91.) according to the manner in which the 

 experiment was made. In the only instance where 

 all the circumstances were perfectly natural, the j 3 

 cubic inches of air which he inspired, lost 0.3 of a 



* Connexion of Life with Respiration, p. 51. 

 f Essay on Respiration, p. 22. 



