104 



respondence by the two methods was almost com- 

 plete *. As there seems no obvious source of in- 

 accuracy in the processes here employed, and their 

 results so remarkably coincide ; and as they present 

 the average bulk deduced from 56 respirations, we 

 may conclude, says Dr Bostockf, that 40 cubic 

 inches is the quantity of air employed in an ordinary 

 act of respiration J . 



86. The difficulty in arriving, by experiment, at 

 certain conclusions respecting the volume of air ta- 

 ken into the lungs in each inspiration, may arise from 

 a difference in the state or capacity of those organs 

 in different individuals ; from the relative vigour or 

 debility of the muscular powers carrying on the re- 

 spiratory function ; from the circumstances in which 

 the animal is placed ; the composition of the air it- 

 self; or the manner in which it is breathed. In 

 many modes of experiment also, the friction be- 

 tween the air and apparatus employed, or the resis- 

 tance which this latter may create to the ordinary 

 process, will greatly vary the result : and considerable 

 errors must likewise have arisen from the variation 

 in bulk, occasioned by the change of temperature, 

 which the air, during'its respiration, suffers ; from the 

 difficulty of breathing in a natural manner when the 



* Menzies on Respiration, p. 21. et seq. 



f- On Respiration, p. 34-. 



J Besides the respectable authorities mentioned in the text, 

 Dr Bostock quotes the names of Blumenbach, Chaptal, Bell, 

 Fontana, and Richerand, as estimating the bulk of a single inspi- 

 ration at between 30 and 4<0 cubic inches of air. 



