690 SYMPATHETIC AND OTHER SYSTEMS OE NERVES. 



Head finds that each area below the brachial gap, when associated with an 

 area above the brachial gap, is associated with the same one ; and, further, that 

 the two associated areas may be the seat of referred pain from disease in different 

 organs, for example, the stomach and the liver. Since each organ receives 

 afferent fibres from more than one white ramus, we might expect that the 

 fibres sometimes of one, sometimes of another, white ramus would be especially 

 affected, and so cause referred pain in a different area of the skin ; but it is 

 difficult to see why there should be any correlated variation in the seat of 

 referred pain above the gap, except on the unlikely supposition that the 

 afferent fibres of each white ramus are connected peripherally with the fibres 

 of a particular strand of the vagus. Head suggests that in some cases the 

 correlation occurs by means of the spinal cord. According to Head, the skin 

 of the third and fourth cervical segments does not become the seat of referred 

 pain from disease of any organ of the head or neck ; when it is affected from 

 disease of the thoracic or abdominal viscera, it has correlated with it an area 

 of pain in the head. 



This correlation of tender areas above and below the brachial gap 

 must, on the view we are taking of the matter, cease when organs are 

 reached which do not receive fibres both from the vagus and the 

 splanchnics. We do not know whether the lowest white ramus to send 

 fibres to the intestines in man is the tenth, eleventh, or twelfth thoracic. 

 All that we can say then, theoretically, is that the tenth, eleventh, or 

 twelfth thoracic segment should be the last to be correlated with a 

 tender region in the head or neck. According to Head, the tenth 

 thoracic segment is the last. 



We might also expect that there would similarly be double areas of 

 referred pain, from disease of the descending colon and of such viscera as 

 receive afferent fibres by way of the sympathetic and by way of the 

 pelvic nerve. Of this, however, we can at present say very little. 



We have taken, as the first step to an explanation, the view that 

 irritation by disease of the afferent fibres of the white ramus of any 

 nerve causes somehow irritation of the cutaneous sensory fibres of the 

 nerve, and that thus tenderness or pain within the skin area of the nerve 

 is produced. 



Some difficulty seems to have been felt in accepting this view, since 

 Head finds that the areas of referred pain and tenderness overlap little 

 or not at all, and Sherrington finds that the sensory areas of the spinal 

 nerves overlap considerably. But that the band of referred pain 

 should be narrower than the band of cutaneous distribution of a nerve, 

 seems natural enough. There is good reason to believe that the edges of 

 the band of cutaneous distribution of a nerve receive fewer fibres than ■ 

 the central portion, and thus the central parts w r ould naturally pass first 

 into a state of over-sensitiveness. In visceral disease, though the fibres ,' 

 of a particular white ramus may be more affected than any other, it can 

 never be affected alone, and it is not unreasonable to suppose that the 

 irritation of other rami reaches the level at which a referred tenderness 

 is produced before the irritation of the first is of such intensity that it 

 causes referred tenderness in the parts of the skin which are but scantily 

 supplied with somatic fibres from the corresponding spinal nerve. 



There is nothing to show that if one ramus alone could be irritated, 

 the region of skin tenderness would not coincide with the region of 

 sensory supply of the somatic fibres of the nerve to which the ramus 

 belongs. It must be mentioned, however, that Head, who has done most 



