CHAPTER XXX. 



SENSATION AND SENSE-OKGANS. 



The Subjective Functions of the Nervous System. 

 Changes in many parts of our Bodies are accompanied or 

 followed by those states of consciousness which we call sen- 

 sations. All such sensitive parts are in connection, direct 

 or indirect, with the brain, by certain afferent nerve-fibres 

 called sensory. Since all feeling is lost in any region of the 

 Body when this connecting path is severed, it is clear that 

 all sensations, whatever their primary exciting cause, are 

 finally dependent on conditions of the central nervous sys- 

 tem. Hitherto we have studied this as its activities are 

 revealed through movements which it excites or prevents; 

 we have seen it, directly or reflexly, cause muscles to con- 

 tract, glands to secrete, or the pulsations of the heart to 

 cease; we have viewed it objectively, as a motion-regulating 

 apparatus. Now we have to turn to another side and con- 

 sider it (or parts of it) as influencing the states of conscious- 

 ness of its possessor: this study of the subjective activities 

 of the nervous system is one of much greater difficulty. 



It may be objected that considerations concerning states 

 of feeling have no proper place in a treatise on Anatomy 

 and Physiology; that, since we cannot form the beginning 

 of a conception how a certain state of the nervous system 

 causes the feeling redness, another the feeling blueness, and 

 a third the emotion anger, all examination of mental phe- 

 nomena should be excluded from the sciences dealing with 

 the structure and properties of living things. But, although 

 we cannot imagine how a nervous state (neurosis) gives rise 

 to a conscious state (psychosis], we do know this, that dis- 

 tinct phenomena of consciousness never come under our 



