SEC. 5. ON THE DEVELOPMENT OF CUTANEOUS AND 

 SOME OTHER SENSATIONS. 



504. The sensations with which we have just dealt arise 

 through impulses passing along special nerves or parts of spe- 

 cial nerves, the optic nerve, the olfactory nerve, &c. ; we have 

 now to deal with sensations arising through impulses along the 

 nerves of the body generally. These are of several kinds. In 

 the first place there are sensations which we may speak of as 

 ' cutaneous sensations,' the impulses giving rise to which are 

 started in the skin covering the body, or in the so-called mucous 

 membrane lining certain passages. These sensations, which as 

 we shall see in dealing with the senses are dependent on the 

 existence of special terminal organs in or near the skin, are 

 sensations of ' touch,' in the narrower meaning of that word, 

 by which we appreciate contact with and pressure on the skin, 

 and the sensations of ' temperature ' which again we may, as 

 we shall see, divide into sensations of ' heat ' and sensations of 

 ' cold.' These sensations may be excited in varying degree by 

 impulses passing along any nerve branches of which are sup- 

 plied to the skin. Then there are the sensations constituting 

 the * muscular sense,' to which we have already referred, and 

 these again may be excited in any nerve having connections 

 with the skeletal muscles. 



As we shall see in dealing with the senses, when a nerve is 

 laid bare and its fibres are stimulated directly either by pres- 

 sure, such as pinching, or by heat, or by cold, or in other ways, 

 the sensations which are caused do not enable us to appreciate 

 whether the stimulation is one of contact or pressure, or of tem- 

 perature, or of some other kind ; we only experience a ' feeling,' 

 which at all events when it reaches a certain intensity we speak 

 of as 'pain.' And we have reason to think that at least from 

 time to time impulses along various nerves give rise to sensations 

 which have been spoken of as those of 'general sensibility,' 

 by which in addition to other sensations, such as those of touch 

 and of the muscular sense, we become aware of changes in the 

 condition and circumstances of our body. When the stimula- 



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