186 CUTANEOUS ANAESTHETICS 



Irritation of the cutaneous nerves by iodine, 

 camphor, cantharides, menthol, or heat will be inter- 

 preted by the spinal segment as a call for local vaso- 

 dilatation, and in responding to the appeal more 

 blood is supplied not only to the skin area but also 

 to the corresponding viscus. As we have seen, the 

 better blood-supply will give some relief, if such 

 relief is possible, to the pain. This is the theory of 

 counter-irritation. 



The practical corollary is that our counter-irritants 

 should be those having a powerful and prolonged 

 effect on the cutaneous nerves. 



REFERENCES. 



REPORT OF B.M.A. COMMITTEE. British Medical Journal, 



(i.), 1909, p. 783. 

 A. RENDLE SHORT AND WALTER SALISBURY, British Medical 



Journal, 1910, (i.), p. 560. 



