A quantitative study of sensitive cutaneous thermoreceptors with C afferent fibres

It has been demonstrated that heating or cooling the cat's skin can elicit a discharge of impulses in slowly-conducting (C) afferent fibres (Iggo, 1958b, 1959a, b; Douglas, Ritchie & Straub, 1959; Douglas & Ritchie, 1959). However, it was not clear whether the C group contained fibres from 'specific' thermoreceptors comparable in sensitivity with those in the cat's tongue (Hensel & Zotterman, 1951 a; Dodt & Zotterman, 1952). Most of the C fibre thermoreceptors hitherto found responded only to rather extreme heating or cooling (Iggo, 1959 a, b) and therefore were possibly concerned with pain. They were relatively insensitive to mechanical stimulation. There are also numerous C fibres which respond both to mild mechanical stimulation and to sudden cooling of the skin (Douglas et al. 1959; Iggo, 1959a). They have been classified as mechanoreceptors by Iggo (1960). In the present investigation sensitive specific cold and warm receptors with afferent C fibres have been found and their behaviour has been studied quantitatively. The opportunity has also been taken to examine quantitatively the responses of C heat receptors (Iggo, 1959b) and of a few C mechanoreceptors to thermal stimulation. A preliminary account of these results has been published (Hensel, Iggo & Witt, 1959).