232 RESPIRATION. 



may be said to be pretty full. The air of the atmosphere 

 consists of a mixture of nitrogen and oxygen, with a 

 slight addition of carbonic acid and of hydrogen gases : 

 100 parts of atmospheric air consist, according to the 

 latest analyses, very constantly of 79 parts of nitrogen, and 

 21 of oxygen ; the admixtures of carbonic acid and hydrogen, 

 on the contrary, are extremely variable in amount ; the 

 carbonic acid has been ascertained to vary between 0,0003 

 and 1,0 per cent. ; the hydrogen may amount to about 

 1 per cent. The air that is expired yields very nearly the 

 same quantity of nitrogen as the air that is inspired; but it 

 contains less oxygen, and a larger quantity of carbonic acid, 

 and also of hydrogen ; it likewise contains some volatile 

 organic matters. The quantities of oxygen and carbonic 

 acid, in the air, have altered relatively during respiration, in 

 suchwise that the volume of the oxygen which has disappeared 

 is rather greater than that of the carbonic acid which has 

 made its appearance. Sir Humphrey Davy breathed during 

 one minute, making 19 inspirations in the time, 161 cubic 

 inches of air, which in 100 parts consisted of 72,7 nitrogen, 



26.3 oxygen, and 1,0 carbonic acid ; and during this time he 

 expired 152 cubic inches of air, of which 100 parts contained 



73.4 nitrogen, 15,1 oxygen, and 1 1,5 carbonic acid. In this ex- 

 periment, consequently, if we disregard the disappearance of 

 9 cubic inches of air and a slight increase of nitrogen, it appears 

 that from the respired air 1 1,2 per cent of oxygen had vanished, 

 and 10,5 per cent, of carbonic acid had appeared. In the 

 experiments of Allen and Pepys, 100 parts of expired air were 

 found to consist of 79 nitrogen, 13 oxygen, and 8 carbonic acid; 

 supposing, therefore, the air which was breathed to have been 

 of the normal constitution, 8 per cent, of oxygen had disap- 

 peared, and rather more than 8 per cent, of carbonic acid had 

 been evolved. Like results were come to by Dulong, Des- 

 pretz, Lavoisier, and Seguin. In the quantity of the absorbed 

 oxygen and of the added carbonic acid, however, the state- 

 ments of the different observers differ. Davy, for example, 

 found that the quantity of the added carbonic acid amounted 

 to from 3,95 to 4,5 per cent. ; in the particular experiment 

 quoted above, it was as much as 10,5 per cent. Allen and 

 Pepys state it at from 8 to 8,5 per cent. ; Berthollet at from 

 5,53 to 13 per cent. ; Menzies at 5 per cent. ; Prout at from 



