' SENSATION AND CONSCIOUSNESS. 279 



ment of which always elicits the conception of sound, 

 others again the excitement of which always results in 

 the conception of taste, and so on. In entire accord- 

 ance with this assumption is the fact that it does not 

 matter what external cause effects the excitement of 

 any one nerve-fibre, but that every excitement of a given 

 nerve-fibre is always followed by a given sensation. 

 Thus, the nerve of sight may be mechanically or elec- 

 trically irritated, with the result of producing a sensa- 

 tion of light ; mechanical or electric irritation of the 

 auditory nerve effects a sound sensation ; electric irri- 

 tation of the nerve of taste effects just such a sensa- 

 tion of taste as does the influence of a tasted substance. 

 It even happens that the exciting cause is situated 

 in the brain itself and directly excites the nerve-cells, 

 and the sensations which are thus elicited are indis- 

 tinguishable from those which are effected through 

 the nerves. To this are due the subjective sensations, 

 hallucinations and so on, which depend on an altera- 

 tion in the character of the blood, or on an increase 

 in the sensitiveness in the nerve-cells. 



Wherever the excitement occurs, whether in the 

 nerve-cells themselves or anywhere in the course of the 

 nerves leading to the cells, consciousness always refers 

 the sensation to the presence of some external cause of 

 excitement. If the nerve of sight is pressed, the 

 patient believes that he sees a light external to his 

 body ; if a nerve of touch is irritated at any point in 

 its course (e.g. the elbow-nerve at the furcation of the 

 elbow-bones), the patient feels something in the 

 nerves distributed in the skin (in our example in the 

 two last fingers, and in the outer edge of the palm of 

 the hand). Our power of conception therefore always 



