i 9 4 THE NERVOUS SYSTEM 



with confidence that they can trace the pain from the caecum 

 to the rectum, and that it follows the actual course of the 

 bowel. 



On the other hand, cases in which abdominal operations 

 have been performed without the use of a general anaesthetic 

 show that the viscera may be clamped, cut or sutured without 

 giving rise to any painful impressions. In a case operated on 

 by Mackenzie without an anaesthetic of any kind, the patient 

 suffered pain periodically, and it was observed that the pain 

 synchronised with peristalsis affecting a clamped portion of 

 small intestine. The patient, however, localised the pain to 

 an area of the abdominal wall several inches removed from 

 the piece of gut in question. It seems highly probable that 

 this was an example of the viscero-sensory reflex, although it 

 is possible that the mal-reference by the patient was owing to 

 lack of localising sense. 



The arm pain in angina pectoris (p. 309) and the testicular 

 pain in renal colic (p. 364) are both undoubtedly referred 

 pains, and it is not illogical to assume that the chest pain in 

 the former and the abdominal pain in the latter are of a 

 similar nature. 



The relation which exists between the nerve-supply of the 

 viscera and the nerve-supply of the skin of the trunk is a 

 further argument in favour of Mackenzie's view that the 

 viscera are insensitive to painful stimuli. When the segments 

 of the spinal medulla which are responsible for the sensory 

 supply of the skin of the thoracic and abdominal parietes 

 are compared with those which are connected with the 

 sympathetic system by means of white rami communicantes 

 (p. 185), it is found that they are practically identical. The 

 lower lumbar nerves give off no white rami to the sympathetic 

 and they are not represented in the skin-supply either of the 

 abdominal wall proper or of the perineum, which forms a 

 part of the abdominal wall. Further, only those sacral nerves 

 which possess white rami communicantes take part in the 

 sensory supply of the perineum and the external genitalia. 



