Destruction of the Memhrana Tympani. 439 
obstruction of the Eustachian tube ; and the operation consists 
in puncturing the membrana tympani. 
The tympanum of the ear is formed like a drum ; and, as a 
drum will produce very little sound, unless air be admitted by 
a hole in its side, so, in the usual state of the ear, the membrana 
tympani cannot perform its office, if air has not free access to 
the cavity of the tympanum. The air, thus essential to hearing, 
passes from the throat to the ear by the Eustachian tube ; so 
that the membrana tympani is placed between two portions of 
air, the one contained in the meatus, the other in the cavity of 
the tympanum. Accordingly, if the Eustachian tube becomes 
obstructed, the air confined in the tympanum being unable to 
yield, the membrana tympani must cease to vibrate ; and thus, 
sound being no longer conveyed to the interior parts of the 
organ, a permanent deafness must ensue. 
There are several causes by which a closure of the Eustachian 
tube may be produced. 
It may arise, first, from a common cold affecting the parts 
contiguous to the orifices of the tube, and thereby preventing 
the free passage of air into the tympanum. The deafness thus 
produced, however, is often merely temporary. But the frequent 
recurrence of such attacks may produce permanent enlargement 
of the tonsils, which, by their pressure on the Eustachian tubes, 
will occasion a permanent deafness. 
In February last, an instance occurred, of a person who had 
thus been rendered deaf since the year 1793; and I have met 
with another instance of deafness from a similar cause. 
Secondly, The scarlet fever occasions ulcers in the throat, 
which, in healing, frequently close the Eustachian tubes, thereby 
producing lasting deafness. 
