318 



THE RESPIRATION 



animal when the thorax is opened. In the collapse of the lungs thus 

 produced, the alveoli are not completely emptied of air, because some 

 becomes pocketed within them and is expelled only when the lungs are 

 compressed under water. 



The volume of the residual air can readily be measured during life 



Maximum inspiration -7 



Complemental air ._ 



Ordijnary inspiration 

 TIDAL AIR 

 Ordinary expiration 



Supplemental air - 



Maximum expiration - 



Residual air - 



. Vital capacity 



Capacity of equilibrium 



Fig. 107. Amounts of air contained by the lungs in various phases of ordinary and of forced 



respiration. (From Waller.) 



Fig. 108. Diagram to show manner of termination of bronchiole in the atria and air sacs. 

 I, Air sacs (respiratory epithelium) ; II, atria (respiratory epithelium) ; III, alveolar ducts (res- 

 piratory epithelium and occasional muscle fibers) ; IV, respiratory bronchioles (partly respiratory 

 and partly cuboidal epithelium and continuous muscle fibers) ; V, bronchiole (cuboidal epithelium 

 and muscle fibers). It is clear from this diagram that there is no definite position in the respira- 

 tory passages where the bronchiolar epithelium (cuboidal) ends and the respiratory epithelium 

 starts. There can therefore be no definite line of demarkation between the air of the dead space 

 and that of the alveoli. Redrawn from Miller (Journal of Morphology, 1913, XXIV, p. 459). 



