THE SKIN AND COMMON SENSATION. 999 



impulses are strong, they overflow from their ordinary channels of direct and 

 facile conduction toward mechanisms of conscious reaction into channels less 

 direct with consciousness, the latter being composed of a greater number of con- 

 ducting neurones than the former. It is well known that the general rule of 

 arrangement in the spinal cord is, that long nerve fibres lie outside, short nerve 

 fibres inside next to the grey matter. Some of these latter are extremely 

 short, and all belong to " relay cells." It is this sheet of short relay fibres, 

 immediately abutting on the grey matter, that pain impulses to judge 

 from experimental and other data especially in one part of their course 

 employ. These short cell-paths, abutting on the spinal grey matter, effect 

 their mutual linkage there. We know summation in connection with 

 the nervous system only as a property attaching to cell-chains,, of ten, it is 

 true, to simple two-link chains. Hence summation may be a function of the 

 transmission of impulses from one cell to another, in short, a function 

 depending on the synapse. It is in accord with this to find that a conducting 

 chain of a particularly high number of links, i.e. built up of more nerve cells 

 than usual, exhibits summation particularly markedly. That is, the inertia of 

 the pain apparatus may be a peculiarity of the reaction of the " pain " nerve cell, 

 or, on the other hand, may be simply the outcome of its consisting of many 

 nerve cells. That pains are badly localised (E. H. Weber), thus painful touches 

 not so well as less painful, harmonises also with the same general conception. 



The physiological apparatus for cutaneous pain takes, as compared 

 with that of other skin senses, a long time to get into movement, and 

 when once moved requires, in comparison with other apparatus, a long 

 time to return to equilibrium. 



Connected with summation must be the phenomenon of delayed pain 

 sensation 1 commonly met with in tabetic cases. The pain produced by a 

 prick with a needle is perceived only after a lapse of an abnormally long time ; 

 even five seconds may intervene between prick and pain. The sensations of 

 touch and pain are thus isolated, a clear interval separating the two. The 

 patient replies to the single prick with a double response "now," followed by 

 "ah !" corresponding with the "touch" and the "pain." Schiff 2 described a 

 similar phenomenon as occurring in experiments where partial transection of 

 the spinal cord has trespassed on the grey matter and narrowed it. According 

 to him, the delay increased proportionally with the encroachment on the grey 

 matter, just as the wave of conduction was delayed in the bell of medusa where 

 the tissue was encroached upon, and the path narrowed, in Eomanes' experi- 

 ments. 3 Compression of a nerve trunk has also the effect of delaying the 

 sensory reaction for which it is afferent. I myself met very marked instances of 

 delay in experiments, 4 when dealing with the analysis of sensory nerves into 

 their separate root components. For instance, the reflex from a digital nerve 

 which received afferent fibres from the seventh and eighth cervical roots, and 

 from the first thoracic, was much delayed in occurrence after section of the fir-st 

 thoracic and eighth cervical dorsal (afferent) roots ; the latency was sometimes 

 more than three seconds. Clinical observation 5 has also detected the delay 

 in injury or disease of peripheral nerves. Schiffs reference of it to narrowing 

 the grey matter is a suggestion applicable, therefore, to only part of the problem. 

 In my own experiments there was similarly a narrowing of the conduction 

 path, but the path was entirely a peripheral one. The explanation is probably 

 connected with the increase of intensity of reaction obtained in so many cases 



1 Osthoff, "Die Verlangsamung d. Schmerz-empf. bei Tabes dorsalis," Erlangen, 1874. 



2 " Musket- u. Nervenphysiologie," Lahr, 1858. 



3 Phil. Trans,, London, 1880; also, "Jelly Fish, Star Fish, and Sea Urchins," 

 London, 1885. 



4 Phil. Trans., London, 1892. 



5 Leyden and Goldscheider, " Erkrank. d. Ruckenmarks," Wien, 1895, Heft 1 ; Noth- 

 nagel's " Specielle Pathol.," Bd. x. 



