CUTANEOUS AND INTERNAL SENSATIONS 



1081 



Few of the internal organs are supplied with tactile nerves. The 

 mucous membrane of the alimentary canal from the upper end of the 

 oesophagus to the junction of the rectum with the anal canal is in- 

 sensitive to tactile stimulation (Hertz). The movements. of a tape- 

 worm in the intestines are not recognized as tactile sensations, nor the 

 movements of the alimentary canal during digestion, nor the rubbing 

 of one muscle on another during its contraction. 



(Kiesow) . 



Pressure is only perceived when it affects two neighbouring areas to 

 a different degree. Thus, the atmospheric pressure, bearing uniformly 

 on the whole surface of the body, causes no sensation ; we are so entirely 

 unconscious of it that it needed the inspiration of genius to discover 

 it, and the persistence of genius to force the discovery on the world. 

 When the finger is dipped in a trough of mercury at its own temperature, 

 no sensation is perceived except a feeling of constriction at the surface 

 of the liquid. The perception of light pressure and of the form and size 

 of objects in contact with the skin is believed to be due to the touch- 

 spots. Deep pressure, however, is appreciated, not by the skin, but 

 through sensory end-organs in deeper structures probably, e.g., 

 Pacini's corpuscles and the muscle-spindles (Fig. 471, p. 1096). 



Sensations of Warmth and Cold. When a body colder or hotter 

 than the skin is placed on it, or when heat is in any other way 



