Sentence:  But first for your Line. First note, that you are to take care that your hair be round and clear, and free from <WSD>galls</WSD>, or scabs, or frets: for a well- chosen, even, clear, round hair, of a kind of glass-colour, will prove as strong as three uneven scabby hairs that are ill-chosen, and full of <WSD>galls</WSD> or unevenness. You shall seldom find a black hair but it is round, but many white are flat and uneven; therefore, if you get a lock of right, round, clear, glass-colour hair, make much of it. 
Meaning of the word marked with <WSD> tags:  (en)  A bump-like imperfection resembling a gall.