Eye injuries and their treatment . ation. The instrument is suspended from the roof by a light steel cablepassing over pulleys to a balancing counterpoise weight. This allowsthe magnet to be moved freely over the operating table (the patientremaining quiescent), and the point introduced into the wound whenrequired. The point is removable, and thus different sizes and shapescan be used. The current may be taken from any source of sufficientpower ; and its amount is regulated by a rheostat which enables theoperator to have the magnet completely under control. The best known of all the great magn
Eye injuries and their treatment . ation. The instrument is suspended from the roof by a light steel cablepassing over pulleys to a balancing counterpoise weight. This allowsthe magnet to be moved freely over the operating table (the patientremaining quiescent), and the point introduced into the wound whenrequired. The point is removable, and thus different sizes and shapescan be used. The current may be taken from any source of sufficientpower ; and its amount is regulated by a rheostat which enables theoperator to have the magnet completely under control. The best known of all the great magnets is the one devised by Haab,who prefers to bring the patient up to the magnet (which is placed in ahorizontal position) and to take full advantage of the natural mobility ofthe head and eye. I prefer to have the patient flat on a table and tobring the magnet to the eye. In the large portable magnet here describedthe instrument is so accurately balanced by the counterpoise that it canbe manipulated with perfect ease. PLATE PENETRATING WOUNDS 85 measurements must be taken. The distance of theanode of the tube from the centre of the eye is aknown quantity, as is also the amount of the displace-ment of the tube on either side of the zero point ofthe graduated scale on the cross bar of the constants being thus obtained, it is easy fromthem to determine the position of the foreign body asmeasured from the centre of the wire cross fixed tothe external orbital margin. 5. The simplest way to determine the position ofthe foreign body in its relation to the antero-posterioraxis of the eyeball is to expose a third plate when theanode of the Crookes tube has been fixed to the zeropoint and set so that the most active rays impingeupon the centre of the wire cross. If the shadows ofthe wire cross and foreign body are afterwards markedon the sheet of celluloid all that needs to be doneis to measure the distance between them. The thirdplate, however, is not necessary,
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