150 A. IGGO 



Specialized basal cell layer was still absent. A few days after this the 

 typical, low threshold, slowly-adapting response to mechanical stimulation 

 reappeared, weakly at first, and with it a response to temperature changes. 

 Coincident with this change was the re-appearance of the specialized 

 epidermal cells, with their enclosed nerve discs and other features. 



From these results it can be concluded that the afferent fibres do not 

 possess any selective sensitivity when they are growing into the skin and 

 that in some way the differentiation of the nerves depends on further 

 development which occurs when the axons have reached their terminal 

 sites. For the afferent fibre innervating a " touch corpuscle " this appears 

 to be the formation of nerve discs in association with specialized cells at 

 the base of the epidermis. Whether this type of differentiation or modula- 

 tion of associated cells by the nerves, or vice versa, occurs with other 

 afferent fibres is not known. The interesting results reported to the 

 Symposium by Dr. Beidler, which establish a progressive change of 

 epithelial cells within the taste bud, suggest that it also occurs there. In 

 general, it can be asked whether the cells associated with the afferent nerve 

 terminals are necessary only for the proper development of their selective 

 sensitivity or whether the selective sensitivity depends more directly on the 

 intervention of the associated cells as transducers. 



REFERENCES 



Brown, A. G. B. and Iggo, A. 1962. /. P/?>.y/o/., in the press. 

 Iggo, a. 1962. Acta Neurovegetativa, in the press. 

 Iggo, A. and Muir, A. R. 1962. /. Anat., in the press. 



