30 Dr. Thomas Thomson [Jan. 



volumes of air, expired from the lungs at 11 o'clock a. m. 

 is 4-24. 



But, from Dr. Prout's experiments, (Annals of Philoso- 

 phy, II., 328; and IV., 331,) it appears that the quantity of 

 carbonic acid gas produced by respiration, is at its maxi- 

 mum at noon, and that its quantity at 11 a. m. is to the 

 mean quantity for 24 hours, as 3*92 to 3*45. It is obvious, 

 from this, that the mean volume of carbonic acid gas in 

 100 volumes of air expired, deduced from the preceding 

 experiments, is 3*72. 



I made a few trials to ascertain how much air different 

 individuals are capable of forcing out of their lungs after a 

 full inspiration. The quantity as might be expected, varies 

 much in different individuals. But when the same indi- 

 vidual repeated the trial, the result was very constantly the 

 same. The following table shows the results : — 



Mr. T. Thomson 150 cubic inches. 



Mr, G. Thomson 163 



Dr. Duncan - 180 



Dr. Thomson 193 



Mr.J.Colquhoun200 



Mr. Coverdale 200 



</ 



200 cubic inches is the most common quantity ; but in one 

 case it amounted to as much as 250. 



The number of respirations in a minute does not vary 

 much in different individuals, being very nearly twenty, or 

 rather between nineteen and twenty. 



I believe that great errors have been committed in the 

 attempts to determine the quantity of air thrown out of the 

 lungs by a common expiration. I am satisfied that the 

 quantity which I pitched upon from the experiments of 

 Menzies, Lavoisier, &c, namely, forty cubic inches is far 

 too high. I find, after a great many trials, (for it is very 

 difficult to make a natural expiration when your attention 

 is called to it,) that the quantity of air which I myself throw 



