RESPIRATION. 6ll 



from the lungs after a full inspiration, was a girl about fifteen 

 years of age. The two who expelled 140 and 163 were my two 

 sons, the first aged fourteen, the second aged twelve. The indi- 

 vidual who expelled only 180 cubic inches was a very thin spare 

 gentleman aged twenty-one. I myself could only expel 193 cu- 

 bic inches from the lungs after a full inspiration. These expe- 

 riments were often repeated with the same individual, and the 

 quantity of air which he was able to expel from the lungs after 

 a full inspiration was always the same. The mean of the whole 

 is 186^ cubic inches, or if we leave out the girl, who only made 

 one trial, as the quantity expelled was so small, the average will 

 be 194 cubic inches; or very nearly the quantity, which I my- 

 self was able to expel from the lungs by a forced expiration af- 

 ter a full inspiration. If to this we add the 108 cubic inches 

 which Allen and Pepys found to remain in the lungs after the 

 full expiration which accompanies death, the quantity of air which 

 the lungs are capable of containing, will be 302 cubic inches. 



The quantity of air employed in respiration during a given 

 time will of course depend upon the number of inspirations and 

 expirations per minute. Now these differ considerably in dif- 

 ferent individuals. Dr Hales reckons them at twenty in a minute. 

 A man on whom Dr Menzies made experiments, breathed only 

 fourteen times in a minute. Sir H. Davy informs us that he 

 made between 26 and 27 in a minute. I myself make about 

 1 9 at an average. The average of all is 20. Now 20 in a mi- 

 nute make 28,800 in 24 hours. 



There is a great diversity in the statements of different expe- 

 rimenters respecting the quantity of air which an ordinary sized 

 man draws into the lungs at a single inspiration, and again ex- 

 pels by an ordinary expiration. Dr Menzies concluded from 

 the mean of 56 trials that the quantity of air drawn into the 

 lungs at each inspiration is about forty cubic inches. And Dr 

 Jurin had long before estimated the quantity at forty cubic inches. 

 The experiments of Allen and Pepys, made with great care and 

 upon a large scale, give the quantity only 16^ cubic inches. Dr 

 Goodwyh reckons it from his own experiments at fourteen cubic 

 inches.* Borelli had previously estimated it at eighteen or twenty 

 cubic inches.f I tried the quantity of air which I myself drew in- 



* Goodwyn on Respiration, p. 34. | As quoted by Menzies in his Thesis. 



