THE LOCAL EXTENSION OF NERVE FIBRES INTO DENERVATED AREAS OF SKIN.

Introduction THE existence of extensive overlap between the cutaneous nerve fibres derived from successive nerve roots was first demonstrated by Sherrington (1893) in a study of residual sensibility after section of one or more roots. Other methods, such as that involving local strychninization of the dorsal spinal roots employed by Dusser de Barenne (1910), have been found to give essentially similar results. The method of antidromic stimulation (originally used by Stricker (1876) and Bayliss (1901)) and the study of residual sensibility after the section of dorsal nerve roots were both employed by Foerster (1936) to determine the extent of each human dermatome, and again the correspondence between the results obtained by both methods was close. The amount of overlap which exists between the peripheral cutaneous nerves of the limbs has been determined by a number of methods, which include anatomical dissection, the successive anesthetization of nerves supplying contiguous areas of skin followed by sensory tests (Woollard et al., 1940), electrical stimulation methods through the intact skin (Thompson et al., 1934), and finally by the analysis of the sensory loss following peripheral nerve injuries in a large series of patients (Foerster, 1917, 1929). The correspondence between the stimulation and anwsthetization methods is reasonably close. On the other hand, the analysis of sensory loss and sweat secretion (Guttmann, 1940) following nerve injuries shows in many cases very large degrees of overlap which are not demonstrated by the other methods. This finding, taken in conjunction with the clinical observation by Pollock (1920) that the areas of sensory loss following nerve injuries shrink circumferentially before any regeneration can have taken place from the central stump, suggests either that the method of recording residual sensibility is not entirely accurate or that a proportion of overlapping nerve fibres do not transmit impulses giving rise to sensations for some time following a nerve lesion (Pollock, 1919). It is also possible that a new growth of fibres from surrounding normal nerves towards the area of sensory loss takes place (Schuh, 191 1, and Weddell and Glees, 1941). The method of staining nerve fibres throughout large whole preparations of skin by local injection of methylene blue (Weddell, 1941) has been applied 206