454 ON SENSATIONS IN GENERAL 



tricity it is evident that the character of the sensation cannot agree in any 

 way with the external cause by which it is produced. 



This conclusion is confirmed by experiments demonstrating that one and 

 the same external cause can produce entirely different sensations, by acting upon 

 different sense organs. Thus, pressure on the skin gives a sensation of pressure 

 or of contact; pressure on the eyeball a sensation of light. When illuminating 

 rays strike the eye, we get a sensation of light; when the same rays, sufficiently 

 strong, strike the skin, they produce a sensation of warmth. The sensation which 

 is aroused by an electric current applied to the eye has an entirely different 

 character from that which one gets when the current is applied to the skin. 



4. Just as sensations have their origin in the brain, so also do they receive 

 their specific character from the cerebral background. A sensation of light, 

 however produced, is, in the last analysis, conditioned by a material change 

 in the brain. It follows that such sensations may arise, when neither the eye 

 nor the optic nerve is stimulated, if only the seat of sensation in the brain is 

 excited in some way, as by a disturbance in the blood supply, etc. 



Herein lies the cause of visual hallucinations. For our subjective experi- 

 ence it is a matter of indifference how this particular place in the brain is roused 

 to activity, whether mediately by the optic nerve or immediately by some process 

 in the brain itself. The sensation of light in the latter case must be just as 

 real for the person experiencing it as a sensation produced in the normal manner 

 by the action of light on the retina. 



What we have said concerning the sensations of sight, will of course apply 

 to those from other senses. 



5. Although all our sensations inclusive of the organic sensations have their 

 origin in the brain, they are not consciously referred to the brain, but are 

 projected outward either to other parts of the body or to the surrounding 

 space. Thus we refer the sensations of touch to the skin ; the sensations of 

 taste to the tongue; those of smell to the space around us, to the nose, or to 

 the mouth; the sensations of sound commonly to the surrounding space, in 

 exceptional cases to the ear; sensation of sight always to the outer world. 



The information concerning the general condition of the body brought to 

 the central nervous system, is likewise projected for the most part to differ- 

 ent organs. This occurs most definitely in the case of pains and motor 

 sensations; but other organic sensations also are referred to peripheral 

 organs e. g., the sensation of thirst to the throat, the sensation of hunger 

 to the stomach, etc. 



Sensations which give us the general feeling of bodily tone, or of good 

 spirits are not projected to any definite organ. Neither are they referred to 

 the brain; they represent rather a general peculiar condition permeating the 

 whole body, which is present to consciousness as depression, vigor, indisposi- 

 tion, comfort, etc. 



From all this it follows that in so far as the nature of our sensation gives 

 us any information of the peculiar external agency by which it is excited, it 

 constitutes a sign rather than a picture of that agency. A picture demands 

 some kind of likeness to the thing pictured, but a sign need bear no resem- 

 blance to the thing signified. The only necessary relation between the two 



