COUNTER-IRRITANTS 55 



remote effects. They relieve or remove congestion and pain, 

 and, by stimulating functional activity, promote repair. It 

 is not always easy, however, to explain how these curative 

 results are produced. 



Heat and cold both relieve tension, and hence pain ; but 

 they produce their effects in different ways. Cold reflexly 

 contracts arteries, constringes the tissues, and hence lessens 

 the quantity of blood flowing to an inflamed part. Warmth 

 dilates capillaries adjacent to the seat of inflammation, and 

 hence relieves stasis of blood and venous congestion. Cold 

 lessens the amoeboid movements of the white corpuscles, 

 but to be effective it must be used in the earlier stages of in- 

 flammation, and continuously for a considerable time. 



A mild blister acts in the same way as a warm poultice, 

 viz., it dilates the congested or inflamed capillary network, 

 and thus relieves congestion, inflammation, and pain. It 

 certainly increases circulation through the part, promoting 

 cell growth and hastening absorption. It thus restores 

 healthy action in most inflamed organs, in swollen glands 

 and joints. 



Irritation or inflammation of the skin surface, as indicated, 

 frequently relieves or removes congestion or inflammation, 

 and pain, but it also has an effect on adjacent or deeper- 

 seated parts. For such purposes blisters are applied in most 

 animals, in sore throat, bronchitis, pleurisy, inflamed joints, 

 etc. In fact, the action of irritants applied to the skin 

 may be described as general or systemic, local on the part 

 to which they are applied, and reflex in subjacent or distal 

 parts. 



The general effects produced by moderate stimulation of 

 sensory nerves are (1) vaso-constriction, with a rise of blood- 

 pressure ; (2) quickening of the heart ; and (3) quickening 

 of respiration with a slight rise of temperature. Excessive 

 stimulation causes great vaso-dilatation, fall of blood 

 pressure, and inhibition of the heart, in other words, a 

 condition similar to ' surgical shock.' The local effects have 

 been described. 



The special reflex action (counter-irritation) in subjacent 

 organs is probably due to a relation between the sensory 

 nerves supplying the stimulated skin area, and the trophic 



