240 NATURAL THEOLOGY. 



pies a larger proportion of the canal, the air is 

 sent forth with a greater impetus than that with 

 which it was inhaled, and the consequence is a 

 gradual tendency of the sputa towards the top of 

 the trachea. In the larynx, the same principle 

 holds ; for as the opening of the glottis enlarges in 

 inspiration, and is straightened in expiration, the 

 sensible glottis, by inducing coughing, gets rid of 

 its encumbrance. Without this change in the 

 calibre of the trachea, the secretions could not 

 reach the upper end of the passage, but would fall 

 back upon the lungs. 



"Experiments have been formerly made by M. 

 Favier, which, although no such view as I now 

 present was then in contemplation, prove how the 

 action of the transverse muscle tends to expel for- 

 eign bodies. The trachea of a large dog being 

 opened, it was attempted to thrust different sub- 

 stances into it during inspiration, but these were 

 always sent out with impetus, and could not be 

 retained. Why the dog could not be thus suffo- 

 cated is apparent : the tube is furnished with this 

 most salutary provision to secure the ready expul- 

 sion of all bodies accidentally inhaled — the air 

 passes inwards by the side of the foreign body, 

 but, in its passage outwards, the circumstances 

 are changed by the diminished calibre of the canal, 

 and the body, like a pellet filling up a tube, must 

 be expelled by the breath." 



We have, perhaps, pushed the inquiry far 



