NATURAL THEOLOGY. 191 



Nevertheless, (which is another particularity- 

 well worthy of notice,) these rings are not com- 

 plete — that is, are not cartilaginous and stiff all 

 round ; but their hinder part, which is contiguous 

 to the gullet, is membranous and soft, easily 

 yielding to the distentions of that organ occasion- 

 ed by the descent of solid food. The same rings 

 are also bevelled off at the upper and lower edges, 

 the better to close upon one another when the 

 trachea is compressed or shortened. 



The constitution of the trachea may suggest 

 likewise another reflection. The membrane which 

 lines its inside is perhaps the most sensible, irri- 

 table membrane of the 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 intromission 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. This capacity of perceiving with 

 such acuteness, this impatience of offence, yet per- 

 fect 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^^ 



^ Our author touches here upon the sensibilities which govern 

 the motions of the chest — a subject which might be enlarged 



