[Illustration: FIG. 89A. SHEEN’S BULLET-PROBE AND FORCEPS.] [Illustration: FIG. 89B. SHEEN’S TELEPHONE BULLET-DETECTOR.] ‘The probe is introduced, and when a metallic foreign body is touched a fall of potential occurs, and the telephone buzzes. It is necessary to point out that no mistakes can be made, as may be the case with a battery in circuit. In using the “auto-telephone probe” the body constitutes an electrolyte, the plate one pole of a voltaic circle, the probe the other; on touching a metallic body different to that of the probe, a difference of potential occurs, and the current ensuing flows through the telephone and is recorded by the diaphragm in the usual way.’[65] If the bullet be not found it should be allowed to remain _in situ_ till such time shall have elapsed as will enable the surgeon to determine whether further operative measures are indicated, time being allowed also for skiagraphy and for the evolvement of another plan of campaign. It is of course a well-known fact that bullets in certain regions of the brain--e. g. the frontal lobe--may exercise but little effect on the individual. Further measures are also indicated when the want of cleanliness of the wound and the anatomical situation of the bullet demand secondary operative procedures. All remote operations are planned according to the localizing symptoms, aided by X-ray photography. After exploration for and removal of the bullet an extensive osseous defect may remain. Opinions differ with respect to the time at which an attempt should be made to remedy the deficiency and as to the operative technique appropriate to the condition. The nature of the wound must always be taken into consideration, for the application of any plate of foreign material is doomed to failure in the event of the slightest degree of suppuration. As a general rule, it may be accepted that it is advisable to postpone such measures till after the primary or early healing of the wound. Further delay, however, tends to allow of the formation of such adhesions as will result in the development of Jacksonian epilepsy, chronic headache, traumatic insanity, &c. The operative features requisite to the interposition of plates between the bone and the scalp, and other measures, are fully detailed in Chapter VI. ‘The _after treatment_ consists in keeping the patient as quiet as possible, and the administration of a fluid diet. In some cases, recurring symptoms pointed to the continued presence of bone fragments; these were usually indicated by signs of irritation, or often by local inflammation, in the latter case infection taking the greatest share in the causation. Such cases needed secondary exploration, and the wonderful success of this operation, even when the wound was evidently infected, was perhaps one of the most striking experiences of surgery in general.’ (Makins.)[66]