If the fluid be cerebro-spinal in nature, the natural inference is that the subarachnoid space is opened up to the exterior, either directly or indirectly along the course of a cranial nerve. A chemical analysis of the fluid will determine the nature thereof, provided that the fluid be collected EARLY. Thus, cerebro-spinal fluid is whilst fluid derived from other rich in chlorides, contains sources contains chlorides, a little or no albumen, but fair amount of albumen, and no shows a trace of a reducing sugar. substance, allied to pyro-catechin, Certain factors, however, must be taken into consideration which diminish the value of these chemical tests, for, though the fluid be cerebro-spinal in nature, the admixture of blood at once interferes with the delicacy of the test. Furthermore, even in the event of a profuse discharge of cerebro-spinal fluid, the first part collected alone contains sugar, the discharge soon becoming nothing more or less than a serous exudation. The fluid is almost certainly cerebro-spinal if the discharge begins within twenty-four hours of the accident, if it be practically colourless, fairly profuse, and continuing for two or three days, perhaps longer. Though the discharge usually originates early, cases are recorded in which the flow commenced some weeks after the accident. The discharge may continue for hours or for weeks. Sir W. Savory recorded a case in which fluid escaped for one month from both ears. The quantity also varies greatly, usually a few ounces, but sometimes many pints. Sir W. MacCormac recorded a case in which 10 pints escaped within five hours. A profuse discharge is due to the fact that, as the original cerebro-spinal fluid drains away, its place in the subarachnoid space is taken by a serous exudation from the cerebral venous system. This exudation occurs as soon as the subarachnoid pressure is sufficiently reduced, the serous exudation progressing till the venous and cerebro-spinal pressures are again equal. As regards the _prognosis_, it is interesting to note that the escape of cerebro-spinal fluid implies of necessity that the subarachnoid space is opened up to the exterior, with all attendant dangers of meningeal infection, yet that the prognosis is generally favourable. One might even go further and state that the prognosis in such cases is rather more favourable than under more ordinary circumstances. Thus, Battle records 36 cases with a mortality of 25 per cent., the general mortality of fractured base being about 44 per cent. My own experience tallies with these statistics. The more favourable result hinges no doubt on the fact that the prolonged outflow tends to wash away organisms existent in the aural and nasal passages.