VERTIGO 



369 



Pleasure. The theoretic status of the sensations of pleasure is more 

 vague and doubtful than is that of pain. It seems probable, however, 

 that pleasure end-organs exist (Fig. 221), for example, in certain parts of 

 the sexual organs. It matters not what these be called, whether genital 

 corpuscles or pleasure end-organs, they are certainly destined to incite 

 to the function to which they are attached through the pleasure they or 

 some other sort of end-organs give rise to. If at the same time, as may 

 well be, they reflexly actuate the varied phenomena of coitus and ejacula- 

 tion it is only in line with the probable action of other various sense- 

 organs throughout the body. They do represent pleasure, and pleasure 

 as a true sensation, distinct from agreeable or pleasant feelings. 



There are other conditions which more or less involve various sense- 

 mechanisms. Among these are tickling and vertigo. About the former 

 little worth saying can be given in this place. 



FIG. 221 



Longitudinal section of an ampulla of the fish Gobius: n, nerve; a, canal; 6, entrance 

 into the common chamber; c, epithelium; d, vibratable "hairs." (Hensen.) 



VERTIGO. 



This sense is of some practical importance. It arises from the dis- 

 turbance of the end-organ of the vestibular branch of the eighth cranial 

 ("auditory") nerve. This end-organ consists of the semicircular 

 canals, the ampullae, and part of the labyrinth connected with the internal 

 ear. This is not properly a sense-organ jn the sense that it furnishes 

 sensation, for no consciousness is attached to its action unless its function 

 (mostly that of maintaining reflexly the head's equilibrium) is disturbed. 

 In proper significance, however, that a sense-organ is a peripheral end- 

 organ of an afferent nerve, this organ is a true sense-organ and vertigo a 

 sense. Moreover it may perhaps, or one part of it, have to do with the 

 perception of noise, as we have seen above. 

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