CHAPTER XXXI. 

 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 system. 

 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 contract, 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 consider it (or parts of 

 it) as influencing the states of consciousness 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 

 observation apart from a nervous system, and so are pre- 

 sumably, in some way, endowments of it; we are, therefore, 

 justified in calling them properties of the nervous system; 



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