480 RESPIRATION 



> 



this problem with the help of Gad's pneumatograph^ which consists 

 of a square box with double walls, the space between them being filled 

 with water (Fig. 249). The cover of this air-chamber is fastened 

 with hinges on one side, but is freely movable along its other three 

 sides. If air is breathed from or into its central compartment, the 

 cover moves down or up, its excursions being registered upon the paper 

 of a slowly revolving kymograph. 



Quantities of Air Respired. — A full grown man inspires and expires 

 about 500 c.c. of air with each respiratory act, the expiratory volume 

 being slightly larger on account of its expansion by heat. This is 

 called the tidal air. By the deepest possible inspiration an additional 

 quantity may be accommodated which amounts to at least 1600 c.c. 

 This is the complemental air. Quite similarly, the most forcible 

 expiration relieves the lungs of about 1600 c.c. of air in addition to 

 the 500 c.c. of tidal air. This amount is designated as the supple- 



Fig. 249. — Gad's Pneumatograph. 



mental air. It is to be noted, however, that even the most forcible 

 expiratory effort does not empty the lungs completely. A certain 

 quantity is always left behind, because the lungs do not collapse 

 even during forced expiration, but remain in a condition of partial 

 distention. This air, which cannot be expelled normally, is the residual 

 air. Its amount has been estimated at 1000 to 1200 c.c.^ Its func- 

 tion, obviously, is to prevent the alveolar walls from collapsing, because 

 in this eventuality very much greater muscular efforts would be re- 

 quired to subject these cells again to a normal degree of inspiratory dis- 

 tention. Furthermore, it must be evident that this partially expanded 

 condition of the lungs favors a free movement of the blood through the 

 pulmonary capillaries. In this connection brief reference should also 

 be made to the fact that the residual air cannot be removed in its 

 entirety even by opening the thorax and by permitting the lungs to 

 collapse. Neither can this end be attained by exerting a gentle 

 pressure upon the surfaces of the excised organ, because the walls 



1 Archiv fiir Anat. und Physiol., 1879, 181. Modifications of this spirometer 

 have been constructed by Durig (Zentralbl. fiir Physiol., xvii, 1904, 258), Gutz- 

 mann (Mediz. Klinik, 1910), and Zwaardemaker (Archiv intern, de laryngologie, 

 1906). 



2 Jacobson, Pfluger's Archiv, xliii, 1888, 236. 



