124 THE SPINAL CORD AND CEREBELLUM 



we may catch a distant echo. We may see a dazzling 

 hght, or we may observe a faint ray or glimmer, and 

 the result in one case differs very much from that in 

 the other. But, nevertheless, one sensory impulse 

 cannot, or can only to a very slight extent, act directly 

 as an augmenting influence on other sensory cells. 

 The augmentation must always, under normal condi- 

 tions, take place in a reflex manner, through the 

 ' increase of impulse centre,' that is to say, and 

 through the vaso-motor centre. The loudest noise 

 will frequently lead to no other effect than a temporary 

 increase in the vibrations of the purely auditory cells. 

 On the other hand, a whisper in the dark may make 

 one tremble with anxiety. It is plain, therefore, that 

 the effect of a sensory stimulus does not depend on its 

 intrinsic force, but on the conditions under which the 

 reflex stimulation is brought about. When, however, 

 many groups of sensory cells — groups representing 

 feeling as well as sensation pure and simple — are all 

 vibrating together, the cells on which the reflex 

 Increase depends are stimulated in a far higher degree, and 

 sensory the general effect is proportionately greater. That 

 ihiefiy'due produced by cells representing the feelings is always 

 lauTes^™^ more intense, and especially reacts upon the heart ; 

 but what the cause of this may be, whether such cells 

 are more numerous or whether they receive a greater 

 supply of blood, no one has as yet been able to deter- 

 mine.* That the intensity of sensation and of the 



* It seems not improbable that our emotions are in reality 

 due, not to the action of separate ' emotional ' cells, but to the 



