THE SKIN AND COMMON SENSATION. 983 



the white rami communicantes. Head shows that affections of the thoracic and 

 abdominal viscera, but not of the pelvic, produce pain and tenderness not only 

 in the body, but also over certain areas of the scalp. These headaches, he finds, 

 stand in direct and constant relation to the position of the area of referred 

 pain and tenderness on the surface of the body. The headache corresponds 

 with this or that dorsal segmental area. The skin areas of referred pain in 

 some cases overlap distinctly but not to the same extent as do the areas of 

 segmental nerves, when delimited by the method of "remaining aesthesia." 1 

 Head 2 includes in his considerations the trophic nerves of the skin. " I do not, 

 therefore, think we shall be far wrong in assuming that trophic nerves 

 to the viscera bear a similar relation to the sensory sympathetic fibres as the 

 trophic nerves to the skin bear to the fibres for pain. If this be so, it will help 

 to explain the effect produced by counter-irritation of the skin on the activity 

 of the viscera. Conversely, it will also explain the occasional improvement in 

 pains of a purely nervous origin by some visceral irritation, e.g. the removal of 

 lightning pains over the first, second, third, and fourth sacral areas (rectum) in 

 a tabetic, by the administration of a purge." 



Another set of referred pains studied by Head, 3 are those in which 

 each organ in the head (nose, eye, ear, teeth, tongue, nostrils, larynx, 

 brain) refers a pain to one or more areas on the surface, where the skin 

 may in consequence become actually tender. Thus lesions, not of the 

 conjunctiva and anterior layer of the cornea, for they cause simply local 

 pain, but of the substantia propria of the cornea, and of all parts of the 

 globus behind it, back to the retina, produce pain, frequently tenderness, 

 of areas of skin over the upper half of the face and the anterior half of 

 the cranium from Head's maxillary to his vertical areas inclusive. 



Again, in the instance of the ear, the nieatus auditorius does not cause 

 referred pain, but local pain purely. Lesions of the membrana tympani 

 and middle ear cause referred pain and tenderness over the hyoid area. 

 Tension in the middle ear, such as occurs in the first stage of otitis media 

 before the membrane is perforated, causes referred pain and superficial ten- 

 derness over the vertical and occasionally over the parietal area of the scalp, 

 in addition to that over the hyoid area. 



Head's discovery of the segmental distribution of the skin areas of 

 hyperalgesia was early confirmed by J. Mackenzie, 4 and by J. Kyri. 5 

 The former has pointed out that the pilomotor nerves over a limited 

 area may be rendered abnormally sensitive by visceral disease, a 

 " goose-skin " reflex becomes more readily elicitable than in health. 

 The pilomotor efferents belong to the sympathetic, issuing by the white 

 rami. 6 The general radiation of a sensation is well exemplified, as J. 

 Miiller pointed out, by the associate sensations of the sexual orgasm. 

 For details of the anatomical distribution of Head's areas, the original 

 papers should be consulted. 7 



The central paths of the pain impulses from the skin and viscera 

 are therefore closely connected with one another. The spinal connec- 

 tions of the nerves for warmth and cold, and for trophic disturbances 

 in the skin, must also be in somewhat close association, especially 



1 Sherrington, Phil. Trans., London, 1892. 



2 Brain, London, 1893, vol. xvi. p. 129. 3 Ibid., 1893, vol. xvi. p. 339, etc. 

 4 Ibid., vol. xvi. pp. 321 and 515. 5 Loc. cit. 



6 Langley and Sherrington, Journ. Physiol., Cambridge and London, 1891, vol. xii. 

 p. 278 ; also Langley, ibid., 1893, vol. xv. p. 176. 



7 Brain, loc. cit. 



