[Illustration: FIG. 188. TYMPANIC MEMBRANE SHOWING INCISION IN ACUTE SUPPURATION OF THE MIDDLE EAR. Usual line of incision; dotted line shows continuance of incision to make a flap opening for drainage.] [Illustration: FIG. 189. LINE OF INCISION IN ACUTE SUPPURATION OF THE ATTIC.] If the patient is not under an anæsthetic, the incision may be made too timidly, the membrane being only scratched. The pain thus inflicted will cause the patient to jerk away the head and probably prevent the membrane from being incised freely. The incision, therefore, must be made in a bold and rapid manner. It is better to make the incision too free than too small. Care must be taken not to plunge in the knife too deeply for fear of wounding the mucous membrane of the inner wall of the tympanic cavity. This may result in adhesions between it and the membrane. Further, cases have been recorded in which a too violent incision has injured or dislodged the ossicles, or in which severe hæmorrhage has occurred, presumably from puncturing the bulb of the jugular vein, which was projecting abnormally through the floor of the tympanic cavity. The two chief causes of failure are insufficient drainage from too small an incision, which may necessitate a further operation, and secondary infection from without. =Results.= In the majority of cases, provided free drainage is established, the discharge ceases and healing of the membrane takes place from within a day or two to four weeks, depending on the character of the case. If the symptoms continue it may become necessary to perform the mastoid operation (see p. 373). ARTIFICIAL PERFORATION OF THE TYMPANIC MEMBRANE The object of the operation is to equalize the pressure within the tympanic cavity and external meatus so as to enable vibrations of sound to be transmitted more readily by the membrane and chain of ossicles to the inner ear. =Indications.= (i) In the case of an extremely calcified membrane which apparently cannot vibrate. (ii) To relieve tinnitus or vertigo which appears to be due to an alteration of tension within the tympanic cavity, the result of an impermeable stricture of the Eustachian tube. (iii) As a means of diagnosis. If the hearing be improved or the subjective symptoms relieved as a result of the artificial opening, then, if the perforation closes (as it probably will do), the surgeon is in a position to suggest some more radical measure, such as ossiculectomy (see p. 351). =Operation.= Two methods are employed: (i) The knife; (ii) The galvano-cautery. The perforation should be made in the postero-inferior quadrant. In favour of the galvano-cautery is the fact that the perforation does not tend to close so rapidly. On the other hand, considerable damage may be done unless it is applied with extreme care. For this reason it is wiser to operate under a general anæsthetic, such as gas and oxygen.