ANIMAL MECHANISM. 289 



When a pin-head is introduced far enough to touch the 

 drum head, an exquisitely acute pain is the conse- 

 quence, from pressing the nerve. 



I have seen men with the membranes ruptured on both 

 sides, which was inferred from the fact, that in smoking, 

 they puffed the fumes, for amusement, out at their ears, 

 yet the sense of hearing, in them, did not appear im- 

 paired. The rationale of this will be subsequently 

 explained. The deafness of old people might in some 

 instances be alleviated by puncturing the membrane, 

 which, by age, has become thickened and inelastic. A 

 distinguished surgeon in England, but a few years since, 

 discovered that by making an opening through the drum 

 head, in peculiar cases, restored the diseased ear, instan- 

 ter : the same operation is now successfully practised in 

 this city. 



No one can be in doubt as respects the office of this 

 membrane: it receives the sonorous rays having a 

 broad surface, and being on the stretch, is put in vibra- 

 tory motion by the slightest pulsations in the air, 

 which it transmits to the still more important apparatus 

 within. 



We have remarked that reptiles and fishes have no 

 discernible external orifice: the external surface ap- 

 pears smooth, as though they were destitute of this 

 valuable sense. Under the skin, however, and in the 

 bone answering to the temporal one in man, there is 

 around hole, growing larger within. This cavity is 

 the tympanum or drum barrel answering to the apart- 

 ment beyond the drum head, in men and quadrupeds, 

 next to be elucidated. The common skin, which is thus 

 drawn over the mouth of the tympanum, acts precisely as 

 the drum head does, vibrating to the least noise, with 

 exceeding nicety. In the economy of reptiles those 

 scavengers of the earth, created to wallow in filth at the 

 threshold of organic life, an external ear or opening, 

 would be soon destroyed, by being filled with mud, 

 gravel or insects. The skin over the frog's ear and the 

 catnelion, is very dense, shining and tremulous. Frogs, 

 particularly, have a splendid circular piece of skin over 

 the tympanum, just back of their large prominent eyes. 



