CH. LIV.] VISCERAL SENSATIONS 777 



it is still often called. It is true that sensory end-organs and 

 nerve-fibres occur in muscles and tendons, which presumably transmit 

 impulses upon change of muscular form or of tendinous strain. But 

 we have experimental evidence that the pressure and movement of joint- 

 surfaces are most important factors in the development of kinsesthetic 

 sensations. The " motorial sense " is thus of very complex origin. 



Visceral Sensations. 



Epicritic sensibility is a special characteristic of the cutaneous 

 area. Protopathic sensibility is found in other parts also, but in 

 most internal structures of the body it is limited to pain. The 

 oesophagus and anal canal alone seem to be endowed with the tempera- 

 ture sense ; the feelings of warmth and cold on swallowing liquids of 

 different temperatures are entirely referable to the upper portion of 

 the alimentary canal. Hertz's recent experiments place this beyond 

 question ; immediately the food has passed into the stomach we are 

 unaware of its temperature except by the warming or cooling of the 

 neighbouring portion of the gullet, or the skin overlying the viscera. 



Pain is the most widely distributed sense in the body, but in 

 internal organs is not localised accurately, and it is here that the 

 "referred pains" in corresponding skin areas (see p. 205) are useful 

 for diagnostic purposes. Pain, however, is not produced in the 

 viscera by handling or even by cutting or burning : it appears to be 

 associated with excessive action, stretching, and with inflammatory 

 conditions which involve the sensitive parietal layer of the peri- 

 toneum. Inflammation of the serous membranes is an exceedingly 

 painful condition for instance, in pleurisy and peritonitis but this 

 condition, per se, does not apparently cause any referred pain or 

 tenderness in cutaneous areas. In connection with the question of 

 referred pain, we must mention the pathological condition known 

 as allochiria. When the skin sensations in any given area are 

 depressed, stimulation of that area may give rise to sensations which 

 are referred to the corresponding area on the other side of the body ; 

 it appears to be a general rule, as Head first pointed out, that the 

 mind projects sensations arising from an area of low sensibility to 

 that area of higher sensibility which is related to it most closely by 

 connections within the central nervous system, and this underlies the 

 causation of referred visceral pains. 



There are, however, special kinds of sensation arising from 

 internal viscera which have no counterpart in the sensations of the 

 cutaneous surface. Of these, hunger and thirst are the most familiar. 



Hunger when slight is termed appetite, and there is some differ- 

 ence of opinion whether the two are separate sensations, or only 

 differ in degree. Appetite is referred to the stomach, and is a 

 normal sensation, which arises at an interval after a meal, and as is 



