OH. XVII.] REFERRED PAIN 205 



their central ends produces neither pain nor reflex action ; and the 

 same is true for the cervical sympathetic. 



On the other hand, excitation of the central ends of the white 

 rami produces reflex movements, especially in involuntary muscles, 

 as is evidenced by a rise of blood-pressure due to constriction of 

 peripheral arteries; this is especially the case with white rami 

 connected with thoracic and abdominal viscera. 



It is therefore deduced from this that the sensory autonomic 

 fibres enter the central nervous system by the white rami, but 

 whether they come into relationship with the cells of either sympa- 

 thetic or spinal ganglia is very uncertain. Possibly the cells of 

 origin are within the spinal cord itself. In the cranial region we 

 have some information especially in connection with the vagus 

 nerves of the existence of afferent fibres, which we shall be studying 

 in detail in connection with the heart and the lungs. 



Referred Pain. Localisation of painful or uncomfortable feelings 

 arising from disorders of internal organs is always very difficult. 

 But they are associated with pains in the skin, and this referred pain, 

 as it is called, often plays an important part in ascertaining the 

 position of internal maladies. Pains arising from intestinal irritation 

 are referred to the skin of the lumbar region in the area supplied by 

 the lower thoracic nerves; pains originating in the stomach are 

 referred to an area of skin above this at the lower margin of the 

 ribs, those from the heart to the shoulder region, and so forth. 



Each viscus appears to be correlated with a definite patch or 

 band of skin ; this may even be tender on pressure. Eoss's sugges- 

 tion that the pain in such case is referred by sensory cutaneous fibres 

 ending in the same segments of the cord as do the afferent fibres 

 from the viscera in question, has been placed beyond doubt by the 

 subsequent work of Mackenzie and of Head. 



