Sentence:  While to the fingers and toes, which are frequently the seat of spontaneous <WSD>festers</WSD>, &c., irritation is kept up [if a hot poultice is applied], the skin is thickened, and rendered less liable to be permeated by matter; the heat is driven down the soft structures to the very bones and joints, and a portion of them may be lost in consequence. 
Meaning of the word marked with <WSD> tags:  A sore or an ulcer of the skin.