2. An incomplete or recovering lesion, when such is accompanied by evidence furnished by the position of the wounds, pain, and signs of irritation of pressure from without, or possibly palpable displacement of parts of the vertebra, that the spinal canal is encroached upon by fragments of bone. 3. Retention of the bullet, accompanied by similar signs to those detailed under 2. In both the latter cases the aid of the X-rays should be invoked before resorting to exploration. Operation, if decided upon, in either of the two latter circumstances, may be performed at any date up to six weeks; but if pressure be the actual source of trouble, it is obvious that the more promptly operation is undertaken the better for early relief and ulterior prognostic chances. In only one case of the whole series I observed did it seem possible to regret the omission of an exploration. CHAPTER IX INJURIES TO THE PERIPHERAL NERVE TRUNKS The occurrence of these injuries has undoubtedly increased in frequency with the employment of bullets of small calibre, and no other class of case more strikingly illustrates the localised nature of the lesions produced by small projectiles of high velocity. Again, no other series of injuries affords such obvious indications of the firm and resistent nature of the cicatricial tissue formed in the process of repair of small-calibre wounds, and in none is the advantage of a conservative and expectant attitude so forcibly impressed upon the surgeon. Implication of the nerves may be primary, or secondary to an injury which left them originally unscathed. _Nature of the anatomical lesions._--In degree these vary in mathematical progression, but the extent of the lesion is not always readily differentiated by the early clinical manifestations, and again the actual damage is not to be estimated by the gross apparent anatomical lesion alone; but, in addition, consists in part in changes of a less easily demonstrable nature, varying with the velocity with which the bullet was travelling and the consequent comparative degree of vibratory force to which the nerve has been subjected. In these injuries, as in those of every part of the nervous system, the degree of velocity appears to gain especial importance both in regard to the general symptoms and the local effect on the functional capacity of the nerve. This is perhaps a fitting place for the introduction of a few further remarks as to the significance of the term 'concussion' in connection with the injuries produced by bullets of small calibre, since the most striking exemplification of the results following the transmission of the vibratory force of the projectile is afforded by the behaviour of the comparatively densely ensheathed and supported peripheral nerves.