454 ON lERITANTS AND COUNTER-IRrvITANTS. 



from and independent of each other, although they generally 

 occur together. 



4. Arterial congestion passes into inflammation when stasis 

 begins to occur in the capillaries. 



5. Stasis is not improbably due, as supposed by the brothers 

 Weber, to coagulation of blood in the capillaries, the coagulation 

 being induced by changes in the tissues composing the walls of 

 the vessels, or immediately surrounding them. 



6. Pain in an inflamed part is probably due to distension of 

 vessels and pressure on nerves by the blood being pumped with 

 violence through the dilated arteries against the obstruction in 

 the capillaries. 



7. Pain may be relieved by lessening tension in various ways : 

 by position — by cold — by warmth — by blood-letting — by counter- 

 irritants. 



8. Cold probably relieves tension by contraction of the arteries 

 going to the inflamed part, warmth by dilating the capillaries of 

 the surrounding parts, and thus drawing away the blood from 

 the seat of inflammation. 



9. At the same time that an irritant causes dilatation of the 

 vessels in the part to which it is applied, it causes contraction 

 of the vessels in other parts of the bod^'. 



10. It is probable that it does not cause contraction in all 

 parts alike, but that definite areas of skin correspond to definite 

 sets of internal vessels. 



11. The relief of pain produced by a blister in pleurisy, 

 pneumonia, or rheumatic inflammation of a joint, is probably 

 due to reflex contraction of the arteries in these parts. 



12. Blisters are useful in lessening congestion in pericarditis, 

 and in relieving the pain of inflamed joints in rheumatism.* 



13. The benefit derived from their use in young persons, 

 especially those suffering from a first attack, is very great. In 

 elderly persons it is inconsiderable. 



14. The beneficial action of a blister in callous ulcer is prob- 

 ably due to the increased supply of blood to the part, induced 

 by its application. 



* Introduced by Dr. Horbert Davies, Lond. Hosp. Rep. 



