NATURAL THEOLOGY. 149 



or solid substance attempts to enter it. Besides both 

 these provisions, the passage into the lungs is made 

 so sensitive to the least touch of any liquid or solid 

 substance, even a drop of water, as to produce 

 a convulsion or cough instantaneously, when a parti- 

 cle of food or drink attempts to go the wrong way, 

 as it is called, and forces it back with violence. 

 The membrane which lines the passage from the 

 glottis into the lungs, anatomists term it the tra- 

 chea, " is perhaps the most sensible and irritable mem- 

 brane of the whole body. It rejects the touch of a 

 crumb of bread, or a drop of water, with a spasm which 

 convulses the whole frame ; yet, left to itself and its 

 proper office, the reception of air alone, nothing can 

 be so quiet. It does not even make itself felt ; a man 

 does not know that he has a trachea. The capacity 

 of perceiving with such acuteness this impatience 

 of offence, yet perfect rest and ease, when let alone 

 are properties one would have thought not likely to 

 reside in the same subject. It is to the junction, 

 however, of these almost inconsistent qualities, in 

 this as well as in some other delicate parts of the 

 body, that we owe our safety and our comfort; our 

 safety to their sensibility, our comfort, to their re- 

 pose." What artist would venture upon so exquisite 

 a piece of mechanism, as that of a valve which 

 should be always opening, under a current of water, 

 and which should never suffer a particle of the water 

 to enter the vessel ! " Reflect how frequently we swal- 

 low, how constantly we breathe. In a city feast, for 



