severe
vibratory concussion may, in fact, be more generally destructive than
those of contusion, and the subsequent effects more prolonged. A certain
length of the affected nerve is apparently completely destroyed as a
conductor of impulses, the connective-tissue element alone remaining
intact. Under these circumstances a nerve, the subject of the most
serious degree of vibratory concussion, which, if cut down upon, may
exhibit no macroscopic change, may take a longer period to recover than
one in which the presence of considerable local thickening points to
direct contact with the bullet, with resulting haemorrhage into the nerve
sheath and perhaps partial gross rupture of nerve fibres.

The therapeutic and prognostic importance of the above remarks, if
correct, is obvious. The course of the nerve is preserved by its intact
connective-tissue framework, and ultimate recovery by a regeneration of
the nerve fibres is more likely to be complete, and will be just as
rapid, if nature be relied on and the nerve be left untouched by the
hand of the surgeon.

It is, I think, undeniable that nerve trunks may escape severe or
irrecoverable injury by lateral displacement. The mere fact that the
trunk itself may be perforated by a slit in its long axis would suggest
the possibility of displacement of the whole structure, and this no
doubt occurred with some frequency. Displacement would naturally be most
frequent in the case of nerves, such as those of the arm, which run long
courses in comparatively loose tissue. In a remarkable case already
narrated, an exploratory operation showed the musculo-spiral nerve in
the upper part of the arm to have been driven into a loop which
projected into, and provisionally closed, an opening in the brachial
artery.

I. _Simple concussion._--Anatomically, or histologically, no information
exists as to the changes which give rise to the often transitory
symptoms dependent on this condition. We are reduced to the same
theories of molecular disturbance and change which have been invoked to
account for similar affections of the central nervous system. The
causation of concussion is, however, materially influenced in its degree
by the velocity of flight of the bullet and consequent severity of the
vibratory force exerted. Hence actual contact of the bullet with the
nerves is not necessary for its production, as is seen in the temporary
complete loss of functional capacity in the limbs in many cases