eby the current is opened and closed automatically at
intervals, so as to cause contraction of the muscles.

_The results_ of primary suture, when it has been performed under
favourable conditions, are usually satisfactory. In a series of cases
investigated by Head and Sherren, the period between the operation and
the first return of sensation averaged 65 days. According to Purves
Stewart protopathic sensation commences to appear in about six weeks and
is completely restored in six months; electric sensation and motor power
reappear together in about six months, and restoration is complete in a
year. When sensation returns, the area of insensibility to pain steadily
diminishes and disappears; sensibility to extremes of temperature
appears soon after; and last of all, after a considerable interval,
there is simultaneous return of appreciation of light touch, moderate
degrees of temperature, and the points of a compass.

A clinical means of estimating how regeneration in a divided nerve is
progressing has been described by Tinel. He found that a tingling
sensation, similar to that experienced in the foot, when it is
recovering from the "sleeping" condition induced by prolonged pressure
on the sciatic nerve from sitting on a hard bench, can be elicited on
percussing over _growing_ axis cylinders. Tapping over the proximal end
of a _newly divided nerve_, _e.g._ the common peroneal behind the head
of the fibula, produces no tingling, but when in about three weeks
axis cylinders begin to grow in the proximal end-bulb, local tingling is
induced by tapping there. The downward growth of the axis cylinders can
be traced by tapping over the distal segment of the nerve, the tingling
sensation being elicited as far down as the young axis cylinders have
reached. When the regeneration of the axis cylinders is complete,
tapping no longer causes tingling. It usually takes about one hundred
days for this stage to be reached.

Tinel's sign is present before voluntary movement, muscular tone, or the
normal electrical reactions reappear.

In cases of complete nerve paralysis that have not been operated upon,
the tingling test is helpful in determining whether or not regeneration
is taking place. Its detection may prevent an unnecessary operation
being performed.

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 a