RESPIRATION. 615 



is 4*16 per cent, of carbonic acid gas in the air expired from the 

 lungs. Now, this does not differ much from 4*24, the average 

 in my own case of ten days at eleven o'clock. I am disposed, 

 therefore, to consider 4*24 per cent, as the average volume of 

 oxygen gas converted into carbonic acid gas at eleven o'clock, or 

 rather between eleven and twelve in the forenoon. 



4. Dr Prout has shown by a number of well-conducted expe- 

 riments on himself, that the proportion of carbonic acid formed 

 at each inspiration is different at different periods of the day. It 

 is at its maximum nearly about noon, and is at its minimum 

 about midnight. It appears farther from his trials that the quan- 

 tity of carbonic acid gas in expired air begins to increase nearly 

 at twilight. The following table exhibits the proportion per cent, 

 of carbonic acid in the air expired from his lungs during every 

 hour of the day. The experiments from which it was deduced 

 were made in August :* 



Carbonic Carbonic 



Hour A. M. acid per cent. Hour p. M. acid per cent- 



6 . 3-43 . 6 . 3-40 



7 . 3-48 . 7 . 3-35 



8 . 3-56 . 8 . 3-32 



9 . 3-66 . 9 . 3-30 



10 . 3-78 . 10 . 3-30 



11 . 3-92 .11 . 3-30 



12 . 4-10 . 12 . 3-30 



1 . 3-98 . 1 . 3-30 



2 . 3-80 . 2 . 3-30 



3 . 3-65 . 3 . 3-30 



4 . 3-54 . 4 . 3*33 



5 . 3-46 . 5 . 3-38 



Mean, 3-45 



Dr Prout found that alcohol and all fermented liquors diminish- 

 ed the proportion of carbonic acid formed by respiration, and this 

 was confirmed by the experiments of Dr A. Fyfe. They found 

 likewise' that when the constitution is affected by mercury, the 

 proportion of carbonic acid gas in the air expired is diminished. 

 Dr Fyfe found that the quantity was likewise diminished by a 

 course of nitric acid, and by a vegetable diet.f Mr Macgregor 



* Annals of Philosophy, ii. 328, and iv. 321. t Ibid. iv. 334. 



