142 A FEW POINTS IN CONNECTION WWH 



Street produce in the epithelial cells of the ear a sense of noise ; 

 but they also produce on the body surface a sense of vibration, 

 transmitted through the earth. Thus, the sense of sight, hearing, 

 smell, taste, and touch are merely modifications of consciousness 

 propagated in different ways around us, capable of being received 

 only by certain portions of our surface, and each producing a par- 

 ticular impression when the stimulus is carried up by the nerves to 

 our brain-cells. And the converse also holds good — namely, that 

 in whatever way those surface-cells are stimulated, the cerebral 

 impression called forth is the one that would be called forth by 

 the usual stimulus affecting them. For example, a blow on the 

 eye produces the sensation in the brain-cells of a flash of light, 

 because the central cells merely receive a stimulus from the eye 

 epithelium, and that is usually due to waves of light. So also in 

 disease, when the surface epithelium is being constantly irritated, 

 there may be, if it is in the ear, noises ; if in the eyes, flashes of 

 light ; or if in the skin, creeping sensations ; and so forth. 



I would next draw your attention to the accuracy of the locali- 

 sation of stimuli on the body surface. Although the seat of the 

 conscious impression is enclosed in the bony skull (and we know 

 that it is so because during sleep, or brain rest, the external 

 stimuli produce no effect); yet when an external stimulus acts upon 

 any part of our surface, the brain-cell not only receives an impres- 

 sion of surface irritation, but we know exactly where on the body 

 surface the irritation has occurred. Thus, if something touches 

 my little finger, I immediately know the exact spot where my 

 finger has been touched, so that I am able at once, if necessary, 

 to move my muscles so as to remove the irritant if it be harmful, 

 or to seize it if it is wanted. There must, therefore, be somewhere 

 in the brain a separate set of nerve-cells representing each square 

 inch of the body surface ; and whenever those are irritated the 

 consciousness projects the impression to its corresponding portion 

 of surface ; something in the way, that if the little brass plate 

 opposite my number in the switch-room of the Central Telephone 

 Office drops, the attendant thinks I have rung, and calls out to 

 know if I am there. Usually 1 have rung ; but if there is some 

 fault in the little brass plate and it falls of itself, the resulting 

 impression on the attendant is the same. 



