CUTANEOUS ANESTHETICS 185 



To carry off and dilute toxins, again, there must be 

 vasodilatation. It is true that in the early stages, 

 before any quantity of exudate has been poured out, 

 and where the cause of the trouble is mechanical 

 injury, not bacterial toxins, the vasoconstriction 

 obtained by cold may prevent the increase of the 

 fluid in the tissues. But when the outpouring has 

 already taken place, we need some means of inducing 

 vasodilatation. 



We need not explain how heat and Bier's bandage 

 will produce this effect, but at once turn to ask why 

 putting irritants on the skin can cause vasodilatation 

 in the deeper parts. 



Each segment of the spinal cord, medulla, pons, and 

 isthmus receives sensory impulses from the skin, 

 and also from a viscus. Messages from the former 

 we can localize accurately. Messages from the 

 latter the segment cannot localize at all, but we 

 know vaguely that the discomfort is in the visceral 

 area which is innervated from that segment. Mis- 

 interpretations are common, and consequently there 

 may be incorrect localizing of a pain, and tenderness 

 of the corresponding skin area when really the viscus 

 is at fault. To quote a few instances, earache 

 without deafness is usually due to a carious lower 

 back molar ; skin tenderness of the right eleventh 

 dorsal area is associated with commencing appendi- 

 citis ; and painful affections of the ovary or testis 

 may cause girdle pain in the tenth dorsal area. 

 The liver, heart, and stomach all have their areas 

 of referred pain. Dr. Head has published much 

 research on these topics. 



