Diagnosis.—­There is seldom any difficulty in recognising the disease.  It is important, however, to exclude the hysterical form of neuralgia, which is characterised by its occurrence earlier in life, by the pain varying in situation, being frequently bilateral, and being more often constant than paroxysmal.

Treatment.—­Before having recourse to the measures described below, it is advisable to give a thorough trial to the medical measures used in the treatment of neuralgia.

The Injection of Alcohol into the Nerve.—­The alcohol acts by destroying the nerve fibres, and must be brought into direct contact with them; if the nerve has been properly struck the injection is followed by complete anaesthesia in the distribution of the nerve.  The relief may last for from six months to three years; if the pain returns, the injection may be repeated.  The strength of the alcohol should be 85 per cent., and the amount injected about 2 c.c.; a general, or preferably a local, anaesthetic (novocain) should be employed (Schlosser); the needle is 8 cm. long, and 0.7 mm. in diameter.  The severe pain which the alcohol causes may be lessened, after the needle has penetrated to the necessary depth, by passing a few cubic centimetres of a 2 per cent. solution of novocain-suprarenin through it before the alcohol is injected.  The treatment by injection of alcohol is superior to the resection of branches of the nerve, for though relapses occur after the treatment with alcohol, renewed freedom from pain may be obtained by its repetition.  The ophthalmic division should not, however, be treated in this manner, for the alcohol may escape into the orbit and endanger other nerves in this region.  Harris recommends the injection of alcohol into the semilunar ganglion.

Operative Treatment.—­This consists in the removal of the affected nerve or nerves, either by resection—­neurectomy; or by a combination of resection with twisting or tearing of the nerve from its central connections—­avulsion.  To prevent the regeneration of the nerve after these operations, the canal of exit through the bone should be obliterated; this is best accomplished by a silver screw-nail driven home by an ordinary screw-driver (Charles H. Mayo).

When the neuralgia involves branches of two or of all three trunks, or when it has recurred after temporary relief following resection of individual branches, the removal of the semilunar ganglion, along with the main trunks of the maxillary and mandibular divisions, should be considered.

The operation is a difficult and serious one, but the results are satisfactory so far as the cure of the neuralgia is concerned.  There is little or no disability from the unilateral paralysis of the muscles of mastication; but on account of the insensitiveness of the cornea, the eye must be protected from irritation, especially during the first month or two after the operation; this may be done by fixing a large watch-glass around the edge of the orbit with adhesive plaster.