FACTORS AFFECTING RECOVERY OF SENSORY FUNCTION AFTER NERVE LESIONS.

MOST of our knowledge of the processes of sensory recovery after nerve lesions is derived from human cases. Indeed, in some ways man is most suitable for such work, because he can give verbal information about the quality of sensation which is felt. But there are many problems which can only be solved by the comparison of recovery under conditions which differ in respect of one variable only, say level of lesion. Human cases are rarely sufficiently comparable to allow this to be done. Complications are introduced by such factors as varying length of nerve that has been crushed, the time between injury and operation, skill of the surgeon, and so on. It is somewhat surprising, therefore, that there has been remarkably little detailed study of sensory recovery in animals. Vanlair (1882 and 1887) studied recovery of sensation on the sole of dogs after various operative procedures, and several workers have used sensory recovery among other signs for testing the suitability of surgical procedures (Takimoto 1917, Huber 1919, Gosset and Bertrand 1938, 'Tangari 1940, Muesch and Roessel 1941). Most of the observations on recovery of sensation following the interruption of a nerve in animals are restricted to a brief statement that recovery of sensation had taken place after a certain time. Such statements are both insufficient and unsatisfactory. It will be seen later that recovery of sensation in a denervated -area is a complex process and only a part of it is due to regeneration of the interrupted nerve. An exact description of the denervated area in which recovery is observed is thus necessary before any conclusions may be drawn. Therefore a clear knowledge of the sensory distribution of various nerves is an essential preliminary to the study of recovery of sensation in animals. In rabbits there is no satisfactory account of the areas innervated by the various peripheral nerves. No doubt the reason for this lack of investigation has been the fear that reflex responses of the animal would not be sufficiently consistent to enable accurate mapping of the sensory state of the skin. However, if properly handled, rabbits may serve as satisfactory " observers." The responses which may be most conveniently used in the rabbit are withdrawal reactions to pin prick stimuli. The work reported here may be said to have three objects: first, to delimit the maximal and autonomous areas of the skin served by various nerves of the lower extremities of the rabbit; secondly, to show the manner in which shrinkage of the insensitive area left after denervation takes place, and the parts played in this shrinkage by (a) recovery in the zone of overlap between the interrupted nerve and the neighbouring nerves; (b) recovery in the autonomous zone of the interrupted nerve; and thirdly, to show how recovery is affected by such factors as the nature of the lesion, its distance from the skin, age of the animal, and infection.