414 



MEMOIKS OF THE NATIONAL ACADEMY OF SCIENCES. 



Tlie reactiou-times were shorter than when the .same poiuts on the skin were electrically- 

 stimulated, and the mean variations of the separate reactions and of the series are less. An 

 exact comparison can not be made, as the esperimeuts on touch and electrical stimulation were 

 not made simultaneously; but we may conclude that the reaction-time on touch is about 10 a 

 shoiter than on electrical stiinnlation. The mean variations are smaller than any liitherto 

 published, although we have omitted no measurements in calculating the averages. As in the 

 case of electrical stimulatioB, the reactiou-times of J and C are nearly the same, those of D being 

 about 30 jier cent longer. 



In the case of tlie shortest reactions followed stimulation of the forefinger or cheek. The 

 two sets on the forefinger made at different times agree closely (105.5 a and lOG.l a). The times 

 for the ui)per and lower arm and for the upper and lower thigh, respectively, are practically the 

 same in all cases. The differences on the arm are: J 1.4 a, and C 0.8 a, the times being shorter on 

 the lower point. On the thigh the time for the upper point was 0.6 a shorter for D, aud 0.8 a 

 longer for C. As in the case of electrical stimulation, we are unable to determine the velocity in 

 the sensory nerve. The time of trausmissiou is in this case exactly counterbalanced by a shorter 

 cerebral refiex for the lower point. In the case of C the time is about 10 a shorter when the fore- 

 finger is stimulated than when the arm is stimulated, and about 1 a shorter for the toe than for 

 the thigh. As before, we find that the cerebral reflex is shortened when the stimulus is applied on 

 the opposite side of the body to a point corresponding to that with which the movement is made. 

 For D the time was shorter when the blow was on the neck than when on the cheek, whereas it 

 was the reverse for C; the differences are, however, small, and we may conclude that the reaction- 

 times to stimulation of the back of the neck and cheek are about the same. The time was tor J 

 20.7 (T, and for C 62.8 a shorter when the movement was made with the hand than when it was 

 made with the foot. This also corresponds with the results of electrical stimulation, C's reaction- 

 with the foot being more delayed than J's or D's. The difference in time is partly due to the time 

 of transmission in the motor tracts of the si)iiial cord, but at least in the case of C it is probably 

 chiefly due to delay in the coordination of the movement. 



With the falling hammer we also made reactions in whicli the force of the blow was varied. 

 In the experiments described above on electrical stimulation and on touch and in researches 

 hitherto published' on the relation between tlie intensity of the stimulus and the length of the 

 reaction-time, the intensity has not been measured. In this case we were able to measure exactly 

 the force of the blow. The hammer always fell 20 cm., and the weight was 60, 30, or 15 grams. 

 The blow from the heaviest weight was just less than painful; from the lightest it was still ([uite 

 strong. The points E and F on the arm and G and H on the thigh were used. The sets, with 

 30 grams stimulus, are the same as those given in the preceding table. 



Table XII. — lieaclioii-iimis on blows of varying intensiti/. Lower and upper arm and lower and upper ihiyli. D, C, and J 



obscrrers. 2,400 reactions. 



'Excepting that on light by Berger and Cattell. IJryan also reported experimeuts at the tueeting of the 

 American Psychological Association (1892) in which the intensity of .sounds was measured, and obtained results 

 corrcspoudiug to those here given. 



