GENERAL CONDITIONS OF BRAIN- ACTIVITY. 85 



stance alone may awaken outward manifestations, but to- 

 gether, i.e. when the strange man is met in tlie dark, the dog 

 will be excited to violent defiance. * Street-hawkers well 

 know the efficacy of summation, for they arrange themselves 

 in a line upon the sidewalk, and the passer often bms from 

 the last one of them, through the effect of the reiterated so- 

 licitation, what he refused to buy from the first in tne row. 

 Aphasia shows many examples of summation. A patient 

 Avho cannot name an object simply shown him, will name it 

 if he touches as well as sees it, etc. 



Instances of summation might be multiplied indefinitely, 

 but it is hardly worth while to forestall subsequent chapters. 

 Those on Instinct, the Stream of Thought, Attention, Dis- 

 crimination, Association, Memory, Esthetics, and Will, will 

 contain numerous exemplifications of the reach of the prin- 

 ciple in the purely psychological field. 



REACTION-TIME. 



One of the lines of experimental investigation most 

 diligently followed of late years is that of the ascertain- 

 ment of the time occupied by nervous events. Helmholtz led 

 oif by discovering the rapidity of the current in the sciatic 

 nerve of the frog. But the methods he used were soon 

 applied to the sensory nerves and the centres, and the 

 results caused much poj^ular scientific admiration when 

 described as measurements of the ' velocity of thought.' 

 The phrase ' quick as thought ' had from time immemorial 

 signified all that was wonderful and eliisive of determina- 

 tion in the line of speed ; and the way in which Science 

 laid her doomful hand upon this mystery reminded people 

 of the day when Franklin first ' eripuit ccelo fulmen,' fore- 



. * See a similar instance in Macli : Beitrage zur Analyse der Empfin- 

 dungen, p. 36, a sparrow being the animal. My young children are afraid 

 of their own pug-dog. if he enters their room uiiev they are in bed and the 

 lights are out. Compare this statement also : " The first question to a 

 peasant seldom proves more than a flapper to rouse the torpid adjustments 

 of his ears. The invariable answer of a Scottish peasant is, ' What's your 

 wull? ' — that of the English, a vacant stare. A second and even a third 

 question may be required to elicit an answer." (R. Fowler : Some Obser- 

 vations on the Mental State of the Blind, and Deaf, and Dumb (Salisbury, 

 1843), p. 14.) 



