The nerve-trunks in the arm--the median, ulnar, and radial (musculo-spiral)--are apt to be damaged in these injuries; in fractures of the lower part of the shaft the radial nerve is specially liable to be implicated. This may occur at the time of the injury, the nerve being contused by the force causing the fracture, or pressed upon by one or other of the fragments, or its fibres may be partly or completely torn across. When there is evidence of nerve injury, the practitioner should draw the attention of the patient to it then and there, and so guard himself against actions for malpraxis should paralysis of the muscles ensue. Later, the nerve may become involved in callus, or be damaged by the pressure of ill-fitting splints. Weakness or paralysis of the extensors of the wrist and hand results, giving rise to the characteristic "wrist-drop." The actions of the muscles should always be tested before applying splints, and each time the apparatus is removed or readjusted, to assure that no undue pressure is being exerted on the nerves. Union takes place in from four to six weeks in adults, and in from three to four weeks in children. Delayed union, or want of union and the formation of a false joint, is more common in fractures of the middle of the shaft of the humerus than in any other long bone--a point to be borne in mind in treatment. Arrest of growth in the bone from injury to the nutrient artery is also said to have occurred. _Treatment._--To restore the alignment of the bone, extension is made on the lower fragment and the ends are manipulated into position. This may necessitate the use of a general anæsthetic, and care must be taken that no soft tissue intervenes between the fragments, as is evidenced radiographically by the persistence of a clear space between the ends even when they appear to be in apposition. In _transverse_ fractures the position may be maintained by a simple ferrule of poroplastic or Gooch-splinting. The elbow is flexed at a right angle, and the forearm supported in a sling midway between pronation and supination. For a few days the limb may be bound to the chest by a broad roller bandage. [Illustration: FIG. 31.--"Cock-up" Splint, for maintaining Dorsiflexion at Wrist.] The splints are removed daily to admit of massage and movement being carried out, and while the splints are off, the patient is allowed to exercise the fingers and wrist. If at the end of four or five weeks, osseous union has not occurred, the reparative process may be hastened by inducing venous congestion by Bier's method. In _oblique and spiral_ fractures it is often necessary to control the shoulder and elbow-joints to prevent re-displacement. This can be done by means of a plaster of Paris case enclosing the upper part of the thorax, together with the upper arm, abducted, and the elbow, at right angles. [Illustration: FIG. 32.--Gooch Splints for Fracture of Shaft of Humerus; and Rectangular Splint to secure Elbow.]