CHAPTER XV. 

 CUTANEOUS AND INTERNAL SENSATIONS. 



According to the older views, the sensory nerves of the skin give 

 sensations of touch. Modern physiology has shown, however, that 

 these nerves mediate at least four different qualities of sensation, 

 namely, pressure, warmth, cold, and pain. Our so-called touch 

 sensations are usually compound, consisting of a pressure and a 

 temperature component and also very frequently an element of 

 muscle sense when muscular efforts are involved, as, for instance, hi 

 measuring weights or resistances. The four sensory qualities enu- 

 merated constitute the cutaneous senses, and they are present, or, 

 to speak more accurately, the nerves through which these senses are 

 mediated are present not only over the general cutaneous surface, 

 but also in those membranes such as the mucous membrane of 

 the mouth and the rectum (stomodeum and proctodeum) which 

 embryologically are formed from the epiblast. The surfaces in the 

 interior of the body, on the contrary, such as the membranes 

 of the alimentary canal, muscles, fasciae, etc., have only 

 nerves of pain, but no sense of touch or temperature. Of these 

 cutaneous senses, three pressure, warmth, and cold may be 

 grouped with the exterior senses, the sensations being projected to 

 the exterior of the body, into the substance causing the stimulation; 

 although, as was mentioned above, the temperature sensations 

 under conditions ^fever, vascular dilatation, etc. may be pro- 

 jected to parts of the skin itself and be felt as changes in ourselves. 

 The temperature sensations are, in fact, projected to the exterior 

 whenever they are combined with pressure sensations, the latter 

 serving, as it were, as the dominant sense. The pain sense, on the 

 other hand, belongs to the group of interior senses, the sensations 

 being always projected into our own body and being felt as changes 

 in ourselves. In the matter of the classification of the cutaneous 

 senses and, indeed, the body senses in general a new point of view 

 has been suggested by Head and Rivers.* These authors made a 

 careful study of the loss of sensations after division of the cutaneous 

 nerves, and of the subsequent gradual and separate return of these 

 sensations following upon suture of the divided ends. They 

 find that in skin areas made completely anesthetic there is present 

 *Head and Rivers, "Brain," 1905, 99. 

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