VOLUME OF INSPIRATION AND EXPIRATION. 749 



is much more useful to recognise that the tidal air varies considerably 

 in different individuals, according to the rate and depth of breathing. 



The complemental air. is the term given to the extra volume of air 

 which can be taken into the lungs by the deepest possible inspiration. 

 Its average value for an adult is said to be 1500 c.c. H. Davy gives 

 1951 c.c., 1 Kite 3280, 2 and Hutchinson 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 Bostock'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, 6 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 observations 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 Pfluger's 13 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. 410. 



2 "Essays and Observations, Physical and Medical," 1795, p. 47. 



3 Article "Thorax," Todd's " Cyclopaedia 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 "Physiologic 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. 



"Researches concerning Nitrous Oxide," London, 1800, p. 399. 



9 Compt. rend. Acad. d. sc., Paris, 1862, tome Iv. p. 279 ; Journ. de Tanat. et physiol. 

 etc., Paris, 1864, tome i. p. 523. 



10 "Lehrbuch der Physiol.," Berlin, 1896, Aufl. 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.f. d. ges. Physiol. , Bonn, 1882, Bd. xxix. S. 244. 



14 For some other results, see Hutchinson, loc. cit. 



