Primary suture should not be attempted so long as the wound shows signs of infection, as it is almost certain to end in failure.  The ends should be sutured, however, as soon as the wound is aseptic or has healed.

#Secondary Suture.#—­The term secondary suture is applied to the operation of stitching the ends of the divided nerve after the wound has healed.

Results of Secondary Suture.—­When secondary suture has been performed under favourable conditions, the prognosis is good, but a longer time is required for restoration of function than after primary suture.  Purves Stewart says protopathic sensation is sometimes observed much earlier than in primary suture, because partial regeneration of axis cylinders in the peripheral segment has already taken place.  Sensation is recovered first, but it seldom returns before three or four months.  There then follows an improvement or disappearance of any trophic disturbances that may be present.  Recovery of motion may be deferred for long periods—­rather because of the changes in the muscles than from want of conductivity in the nerve—­and if the muscles have undergone complete degeneration, it may never take place at all.  While waiting for recovery, every effort should be made to maintain the nutrition of the damaged nerve, and of the parts which it supplies.

When suture is found to be impossible, recourse must be had to other methods, known as nerve bridging and nerve implantation.

#Incomplete Division of a Mixed Nerve.#—­The effects of partial division of a mixed nerve vary according to the destination of the nerve bundles that have been interrupted.  Within their area of distribution the paralysis is as complete as if the whole trunk had been cut across.  The uninjured nerve-bundles continue to transmit impulses with the result that there is a dissociated paralysis within the distribution of the affected nerve, some muscles continuing to act and to respond normally to electric stimulation, while others behave as if the whole nerve-trunk had been severed.

In addition to vasomotor and trophic changes, there is often severe pain of a burning kind (causalgia or thermalgia) which comes on about a fortnight after the injury and causes intense and continuous suffering which may last for months.  Paroxysms of pain may be excited by the slightest touch or by heat, and the patient usually learns for himself that the constant application of cold wet cloths allays the pain.  The thermalgic area sweats profusely.

Operative treatment is indicated where there is no sign of improvement within three months, when recovery is arrested before complete restoration of function is attained, or when thermalgic pain is excessive.