9 88 CUTANEOUS SENSATIONS. 



with little or no diminution in sensibility to contact, with intact "motor" 

 sensations and normal localisation. 1 But, as a fact, other combinations of 

 selective loss not unfrequently occur, for which mere gradation of injury is 

 not so plausible an explanation ; thus, complete loss of temperature sensations 

 in forearm and hand, with pain and contact preserved, due to injury of the 

 shoulder. 2 On reunion of a cutaneous nerve trunk after trauma, the different 

 specific sensations return at different rates, usually cold before pain and pain 

 before warmth. 3 An exhaustive and most interesting analysis of the changes 

 in the sense spots of the arm, due to pressure of a cervical rib on the 

 brachial plexus, has been described from the case of himself by L. F. Barker. 4 

 He found groups of sense spots of one kind persisting in places where none of 

 other sense species remained. Most of the sense spots in these selectively 

 anaesthetic areas reacted to normal threshold stimuli, as could be particularly 

 well proved for the pain spots. In places " cold pain " and " warmth pain " 

 were elicitable, but not "cold" or "warmth" sensation; that is, ice gave 

 pain but no cold, a heat of 47° C. also pain but no " warmth " sensation. 5 

 The skin had thus in so far been transmuted to the sensory condition of the 

 mucosa of the stomach, where the ice that is painfully cold to the lips causes 

 pain but no sensation whatsoever of cold. 



In toxic neuritis, 6 and in tabes dorsalis, as well as in the above pressure 

 diseases, the injury to the peripheral nerves may act selectively in regard to 

 the pain spots. 



It would seem that we may with some probability allocate the pain sense 

 to certain kinds of the multifold structures described as nerve-endings in the 

 skin — (1) The pain-endings lie more superficially than the other endings. This 

 is strongly indicated by the lowness of their threshold electrical stimulus, 

 which cannot be due to a greater electrical excitability of the pain nerve 

 fibres, since when the ulnar trunk is galvanised the touch fibres are the 

 most easily excited. (2) The central part of the cornea appears to be endowed 

 with pain sensation only. It is found to possess histologically only one form 

 of nerve-ending, namely, free nerve filaments ramifying amidst the epithelial 

 cells. It is therefore probable that the free nerve filaments 7 in the epidermis 

 form the apparatus. 



For the present issue the two most distinctive differences between 

 the sensory reactions obtainable at touch spots and pain spots re- 

 spectively seem (1) the (not universally accepted) absence of painful 

 quality from the maximal reactions of touch spots ; (2) the relatively 

 poor tactual quality of the reactions excited at pain spots, although 

 even the minimal reaction is there said to possess painful quality. I 

 cannot unhesitatingly find in my own perceptions that excitation of 

 a pain spot, e.g. by a bristle resthesiometer, ever evokes pain pure 

 without any tactual sensation. The fact that there coexist in the skin 

 two kinds of sense spots, excitable by the same sort of mechanical 

 stimulus, and that the one kind requires for excitation a very distinctly 



1 A. Herzen, Arch. f. d. ges. Physiol, Bonn, 1886, Bd. xxxvii. ; E. Biernacki, ref. in 

 Neurol. Centralbl., Leipzig, 1893, Bd. xii. S. 369. 



2 Pick, Prag. vied. Wchuschr., 1888. Bd. xiii. S. 81. 



3 Charcot, Compt. rend. Soc. de biol., Paris, 1892, p. 941. 



4 Joum. Exper. Med., N. Y., 1896, vol. i. 



5 For a number of cases of lepra nervosa exhibiting selective sensory paralyses, see 

 Laehr, Arch. f. Psychiat., Berlin, 1897, Bd. xxviii. S. 772; Pitres, Gaz. d. h6p., Paris, 

 1892, tome Ixv. p. 1287 ; Rosenbach, Neurol. Centralbl.. Leipzig, 1884, Bd. iii. S. 361 ; 

 H. Schlesinger, Deutsche Ztschr. f. Nervenh., Leipzig, 1892,' Bd. ii. S. 230 ; Marestant, Ben. 

 de mid., Paris, 1891, tome xi. p. 781 ; Thibierge Bruhl, Gaz. held, de mid., Paris, 1891. 



6 See Beau, Arch. gin. de mid., Paris, 1848, tome lxxvi. 



7 Merkel, Arch. f. mikr. Anat., Bonn, 1875, Bd. xi. S. 636 ; Ranvier, Compt. rend. 

 Soc. de biol., Paris, 1880, tome xli. p. 1087; Dogiel, Arch. f. mikr. Anat., Bonn, 1891, 

 Bd. xxxvii. S. 602 ; 1893, Bd. xli. S. 585. 



