CHAPTER XVIII 



ORGANIC SENSATIONS 



WE include as organic sensations all those sensations aroused independently 

 of external stimuli by internal processes going on in the various peripheral 

 organs. Sensations excited from the sense organs normally by external agen- 

 cies or abnormally by pathological processes evidently do not belong in this 

 category. 



Among the sensations thus defined we may mention first those which con- 

 stitute the source of our general bodily feelings (page 452). But analysis of 

 this class of sensations has not progressed far enough as yet to entitle them 

 to further consideration here. We should mention also certain occasional 

 sensations of pain arising within the internal organs concerning the exact 

 cause of which nothing positive is yet known. 



The only organic sensations thus far studied critically are those by which 

 we form ideas of the position of our bodies and their parts (head, trunk and 

 extremities) in space, and those by which we are made aware of the extent, 

 intensity and direction of our movements. These sensations play a consider- 

 able part in the regulation of our movements and besides are very important 

 in the psychological elaboration of our sense impressions (even of those -which 

 arise through external agencies), although they appear as a rule to be indis- 

 tinct and indefinite in comparison with the last named. 



The two groups of organic sensations just mentioned are not, however, 

 everywhere sharply distinct from one another. The impulses by which we 

 are made aware of our bodily movements, their direction and intensity, merge 

 into the less distinct afferent impulses by which we form ideas concerning 

 the orientation of our bodies. The anatomical substratum of our motor sensa- 

 tions and of our sense of position is furnished in part by the sensory nerve 

 endings of the muscles, tendons, joints, skin and in part by those of certain 

 portions of the inner ear (semicircular canals and otolith sacs). 



1. MOTOR SENSATIONS 



Even with the eyes closed we have a very definite idea of the position of 

 our limbs. If, for example, one arm be passively placed in a certain position, 

 the person can with his eyes closed place the other arm in exactly the same 

 position. Likewise a person has a perfectly precise idea with respect both to 

 direction and speed of the changes in the position of his limbs. Finally, one 

 can estimate weights very accurately by lifting them. 



These and other similar sensations are described by different authors by 

 different names, such as motor sensations, muscular sense, sense of force, etc. 



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