In the large nerve-trunks of the limbs he has worked out the exact position of the bundles for the various groups of muscles, so that in a cross section of a particular nerve the component bundles can be labelled as confidently and accurately as can be the cortical areas in the brain.  In the living subject, by using a fine needle-like electrode and a very weak galvanic current, he has been able to differentiate the nerve bundles for the various groups of muscles.  In several cases of spastic paralysis he succeeded in picking out in the nerve-trunk of the affected limb the nerve bundles supplying the spastic muscles, and, by resecting portions of them, in relieving the spasm.  In a case of spastic contracture of the pronator muscles of the forearm, for example, an incision is made along the line of the median nerve above the bend of the elbow.  At the lateral side of the median nerve, where it lies in contact with the biceps muscle, is situated a well-defined and easily isolated bundle of fibres which supplies the pronator teres, the flexor carpi radialis, and the palmaris longus muscles.  On incising the sheath of the nerve this bundle can be readily dissected up and its identity confirmed by stimulating it with a very weak galvanic current.  An inch or more of the bundle is then resected.

INJURIES OF NERVES

Nerves are liable to be cut or torn across, bruised, compressed, stretched, or torn away from their connections with the spinal medulla.

#Complete Division of a Mixed Nerve.#—­Complete division is a common result of accidental wounds, especially above the wrist, where the ulnar, median, and radial nerves are frequently cut across, and in gun-shot injuries.

Changes in Structure and Function.—­The mere interruption of the continuity of a nerve results in degeneration of its fibres, the myelin being broken up into droplets and absorbed, while the axis cylinders swell up, disintegrate, and finally disappear.  Both the conducting and the insulating elements are thus lost.  The degeneration in the central end of the divided nerve is usually limited to the immediate proximity of the lesion, and does not even involve all the nerve fibres.  In the distal end, it extends throughout the entire peripheral distribution of the nerve, and appears to be due to the cutting off of the fibres from their trophic nerve cells in the spinal medulla.  Immediate suturing of the ends does not affect the degeneration of the distal segment.  The peripheral end undergoes complete degeneration in from six weeks to two months.

The physiological effects of complete division are that the muscles supplied by the nerve are immediately paralysed, the area to which it furnishes the sole cutaneous supply becomes insensitive, and the other structures, including tendons, bones, and joints, lose sensation, and begin to atrophy from loss of the trophic influence.