MEMOIRS OK Till-. NATIONAL ACADEMY OF SCIENCES. 



407 



Taisle II. — lUacHon-timvs on elfclrical stiniiilatioii. 1> <iii<l ,1 nbno-ririi. ^.SfMreaclious. 



Tbe tt)t:il time of ten reactions was measured, excepting in the first, .second, tliird, and eighth sets, in which 

 "the reactions were measured .singly. In these sets tho mean variation of tlie single reactions from the series to 

 which they belong was for .1, 9.7 6: C, 8.7 (J. 



The experiineuts do not discover any markftd dittereiice in the time of reaction wlien the 

 shock was applied to the skin by electrodes 5 mm. apart, when the electrodes were on opposite 

 sides of the limb, and when the current was conducted through the body to the foot. In the two 

 sets in which the differences were directly compared the times were l.fi ff and 4.3 ff .shorter when 

 the current passed through the limb than when it was applied simply to the skin. The .sensation 

 is more intense when the shock is applied through electrodes close together, and more nia.^slrc when 

 they are farther apart. This is a psychological distinction of some importance. One sensation 

 would be greater than another either because it is more intense, the same nervous elements being 

 more activelj^ stimulated, or more massive, more nervous elements being stimulated. When the 

 points A and B were stimulated — A being slightly the more distant from tlie brain — the reaction- 

 time on A was the shorter, the differences being, for C, 0.9, 7..3, .">, 11.3, lii.C, 0.8, and —1.9 (T: for 

 ,T. 2 and 3.7 ff; on the average. 4.C (>. The shorter time for the point D is due to the greater 

 massiveness of the shock or the different nerve supply and cerebral connections. It is, con- 

 se(iuently, evident that the leactiou-time from the same physical stimulus applied to diiferent 

 ])oiiits on the skin does not of necessity measure the velocity of the im])nlse in the plain nerve. 

 When the shock was applied on A and I), at which points the (piality of the shock was nearly 

 the same, the times were nearly alike — 11G.7 a and 117 a — and when a ohms resistance was i^laced 

 in the current giving the shocjc on 1) (in order to make the intensities the same) the times were 

 A 122.7 ff, and D 125 a. 



The experiments given in Table II were preliminary to a more thorough investigation of the 

 variation in the reaction-time according to the point to which the stimulus was applied and its 

 intensity. We took the four points in the arm marked (in fig. 7) A, B, C, and D, and made a large 

 number of reactions on each of these points, the jihysitial stimulus being always the same. As 

 already stated, the sensation was not the same either in intensity or (luality. The ciuality of 

 sensation was mitch alike for A and D, massive as from a blow, and for C and B more piercing. 

 This difterence is accounted for by the intervening muscle in the case of A and D and the muscular 

 contractions which followed stimulation of these points. The intensity of .sensation was not, 

 however, alike for A and 1 > and fm' B and C, respectively. A further and unexpected complication 

 occurred, the relative intensities not being the same for the two observers who took part in the 

 exi)criments. In the case of C the order of intensity was D, A, C, B, the diftereuces between D 

 and A and between C and B being large. A and C were nearly alike in intensity, but the difference 

 in ([iiality made it dififlcult to compare the inten.sities. The shock from eight cells in pairs on D was 

 nearly the same as from twenty-eight cells on A: that from fourteen cells on A or C was nearly the 

 same as from tweuty-eight cells on B. In the case of J the order of intensity was A, D. B, C, but 

 the diftereuces were not large and seemed to vary from time to time. The results of these experi- 

 ments are given ou Table 111. 



