VOL UME OF INSPIRA TION AND EXJ'IR. I 7 ION. 749 
is much more useful to recognise Ilia I the tidal air varies considerably 
in different individuals, according to the rate and depth of breathing. 
The complemental air is the term giveri to the extra volume of air 
which can be taken into the lungs by the deepesl possible inspiration. 
Its average value for an adult is said to be 1500 c.c. H. Davy gives 
1951 c.c, 1 Kite 3280,- and Eutchinson 1722-1804 c.c. 3 
The reserve or supplemental air is the volume of air which can be 
expelled after an ordinary expiration by a forcible and deep expiration. 
This is, according to linstock's 4 determinations, 2624 c.c. (160 cub. in.), 
while J. Bell 5 gives 1148 c.c. (70 cub. in.), H. Davy, 1263 c.c. (77 cub. 
in.), Hutchinson) 1148-1804 c.c. (70-110 cub. in.), and Vierordt, 1226 c.c. 
The residual air is the air which remains in the lungs after the 
most forcible expiration ; it cannot be driven out of the lungs during 
life. The methods 7 employed to determine this volume of air are of 
two kinds, those for observal ions on the dead, and those for observations 
upon the living body. In the first case, the thorax of the corpse is 
forcibly placed in the position of a deep expiration, and then the air in 
the lungs is measured. For the determination of the residual air of the 
living subject, H. Davy 8 introduced an ingenious method ; he found 
by experiment that hydrogen underwent no appreciable change in the 
lungs, and that it quickly diffused throughout the residual air; he 
therefore respired a quantity of this gas in a gasometer, and then made 
a forced expiration, the air of which was analysed. From the quantity 
of hydrogen left in the lungs, Davy calculated the total quantity of air 
in the thorax at the end of the forced expiration, and found it to be 
672 c.c. (41 cub. in.). This method has been used by Grehant, 9 and in 
a modified form by Hermann 10 and Berenstein. 11 Several factors have 
to be taken into account, such as the absorption of hydrogen by the 
blood, 12 and its diffusion in the residual air. 
Another but less reliable method is Pfliiger's 1:; pneumonometer. The subject 
of the experiment, placed in a special chamber, keeps the chest, as far as 
possible, in the position of a forced expiration, the pressure outside the body 
is then lowered by a known amount, and the lungs passively give off a certain 
quantity of air ; this volume is measured, and from it and the alteration in 
pressure the residual air is calculated. The difficulty is to keep the chest in 
one position during the experiment. 
The results obtained by different observers are given in the follow- 
ing table : u — ■ 
1 "Chem. and Phil. Remarks," p. -110. 
2 "Essays and Observations, Physical and Medical," 1795, p. 47. 
3 Article "Thorax," Todd's " Cyclopedia of Anatomy and Physiology," vol. iv. p. 1067. 
4 "An Elementary System of Physiology," London, 2nd edition, 1828, vol. ii. p. 25. 
5 " Anatomy," vol. i. p. 193. 
6 "Physiologie des Athmens," Karlsruhe, 1845. 
7 For further details of different methods, see Jacobson, "Beitrage zur Frage nach dem 
Beitr. der Residualluft, " Diss., Konigsberg, 1887; and Berenstein, " Ein Beitr. z. Bestim- 
mung der Residualluft, " Diss., Dorpat, 1891. 
8 "Researches concerning Nitrous Oxide," London, 1800, p. 399. 
9 Compt. rend. Acad. d. sc, Paris, 1862, tome lv. p. 279 ; Journ. de I'anat. el physiol. 
etc., Paris, 1864, tome i. p. 523. 
10 "Lehrbuch der Physiol.," Berlin, 1896, Auft. 11, S. 126. 
11 Arch. f. d. ges. Physiol., Bonn, 1891, Bd. 1. S. 363. 
12 Zuntz, Hermann's "Handbuch," Bd. iv., Th. 2, S. 102. 
13 Arch./, d. ges. Physiol., Bonn, 1882, Bd. xxix. S. 244. 
14 For some other results, see Hutchinson, loc. cit. 
