998 CUTANEOUS SENSATIONS. 



Pain sensations summate at less frequency than touch sensations, 

 and even more easily than muscle twitches. 



Richet 1 has pointed out that, in faradising the skin, a distance of the 

 secondary coil from the primary can he found at which neither single make- 

 shocks nor break-shocks are perceptible, but a rapid series of these individually 

 imperceptible shocks evokes a strongly unpleasant sensation. In certain clinical 

 cases, 2 rhythmic repetition of a liminal stimulus, e.g. touches with a brush or 

 needle point, after a certain number of seconds, evokes a pain which swells wave- 

 like to a crisis and then subsides, often recrudescing to a second or even third 

 crisis. When the point of a pin is lightly pressed on the skin, there succeeds, 

 after the immediate pricking feeling, an interval without sensation, followed by 

 a second pricking feeling. This second sensation, which has been termed the 

 " secondary," differs from the first in having no touch-quality mixed with it ; it 

 seems "to come from within." No "secondary sensation" follows stimulation 

 with a single induction shock ; it does, however, follow when a short series, or 

 even two induction shocks, 3 are applied for not less than T V of a second. It is 

 therefore due to summation in the latter case, and probably in the former also. 



The inertia of the organs for pain seems peculiarly great. Faradic ex- 

 citation, with shocks at higher rate of frequency than 20 per second, causes 

 continuous sensation of pain, and the period of latent excitation for pain is 

 relatively long. I found that by focussing the heat-rays from a lamp upon a 

 skin area of about 25 sq. mm. (on the back of the hand), and allowing a per- 

 forated screen to intermittently intercept the radiation, the heat-pain begins to 

 be perceptibly intermittent when, the times of play and of interception being 

 equal, the intermittence falls below the rate of thirteen per minute. An 

 intensity of this intermittent radiation stimuli, at first not painful and 

 yielding sensations strikingly discrete, soon becomes dolorific, and then the 

 sensations remain discrete no longer but are fused more or less together. 



Weber 4 counted the seconds elapsing before the finger- or tongue-tip had 

 to be withdrawn on account of pain from water at various temperatures. The 

 warmth gradually became painful in many instances when not so at first, — e.g. 

 with water at 44° Reaumur, whence the finger was withdrawn in from twenty- 

 one to twenty-eight seconds. He found the fingers of the left hand slightly 

 more sensitive than those of the right. The rounded end of an iron rod, four 

 Paris lines (^ in.) thick, cooled to 3° - 2 Reaumur, and applied to the forehead 

 eleven lines from the median plane evoked painful sensation in ten seconds ; 

 that is, the sensation caused began to be painful in ten seconds, and similarly, 

 from the upper eyelid, in eight seconds became insufferable. In these cases 

 pain almost is summation. 



' When all the spinal paths are in normal condition, impulses of moderate 

 strength will take the simple white paths, and only impulses of excessive 

 strength will overfloAv into the branching side paths through the grey matter." 5 

 The essential part of this idea is (1) a summating path offering high resistance 

 to conduction, and (2) a low resistance path of more mobile neural protoplasm, 

 possessing less inertia. To identify the one with grey matter, the other with 

 white, seems unnecessary and unfortunate. Every conduction path in the 

 nervous system is composed both of grey and white matter, inasmuch as every 

 nerve fibre is but the process of a nerve cell, and every nervous impulse is but 

 a wave of change which travels a concatenation of nerve cells, and every (or 

 almost every) synapse between nerve cells occurs in the grey matter. It is 

 more useful to interpret the suggestion rather in the sense that when nervous 



1 "Recherches expt?r. et cliniques sur la sensibility," Paris, 1877. 



2 Naunyn, Arch. f. cxper. Path. u. Pharrnakol., Leipzig, 1889, Bd. xv. ; and Rosenbach. 



3 Goldselieider and Gad, Arch. f. Physiol., Leipzig, 1892. 

 ••Wagner's " Handworterbuch," 1846, Bd. iii. Abth. 2, S. 481. 



6 Wundt, "Physiol. Psychologie, " 3te Aufl., Bd. i. S. 112; Goldscheider, "Ueberden 

 Schmerz," Berlin, 1894. 



