RESPIRATION . 39 



quotient had been noticed by us before this in the work of the 

 Pike's Peak Expedition (to be referred to later), but had not been 

 explained. It is quite evident from the table that the composition 

 of the deep alveolar air cannot be even approximately calculated 

 from that of the expired air by assuming the existence of a con- 

 stant dead space. The latter assumption has caused great confusion 

 in recent years, particularly in the work of the Copenhagen School. 

 It was shown by Yandell Henderson and his coadjutors that 

 when air passes along an air passage the axial stream is much 

 faster than the peripheral stream, and that as a consequence of 

 this the air in the dead space is not pushed out bodily in front of 

 the alveolar air during expiration. Some of the tracheal and 

 bronchial air is at first left behind, and before pure alveolar air 

 issues at the nose or mouth the air passages have to be washed out 

 by three or four times their volume of alveolar air. This is illus- 



;r : '^ 



Figure 9. 



(a) Shows a "spike" of smoke moving through a glass tube, (b) 

 Shows the condition when the current is suddenly stopped and mixing 

 instantaneously occurs, (c) Shows clear air drawn in. 



Figure 10. 



Shows how a column of smoke crosses a bulb with little mixing 

 or sweeping out of the air within it. 



trated by Figures 9 and 10, taken from their paper, and drawn 

 from experiments made with smoke. Both they and I found also 

 that a pause before expiration diminishes the volume of the ap- 

 parent dead space. This is easily understood, as the air in the 

 atria, etc., will during the pause come nearer in composition to 

 that of the saccular alveoli. With care in avoiding a pause I found 



