If the imposthume come from matter poured from member to member,387 it comes suddenly, and if from excess of nourishment388 in the member, it comes slowly, by degrees. If the imposthumes be compound, they will have compound signs, according to the humours of which they are formed. If sanguine humour be responsible, and be strongest therein, the colour of the imposthume will turn to dull red.389 If choler dominate, it turns to bright red unless it become purulent. If salt phlegm be strongest therein, it will become white, with a kind of yellowness, because of the mixing of phlegm with choler, for choler is bright when it is not mixed with any other
p.179humour: usually there is itching in the place wherein is salt phlegm. If melancholy be strongest, the colour is black and blue and heaviness, insensibility, and great hardness are present, for if there be sensation it would not be formed from pure melancholy. No imposthume is formed from pure melancholy, but from dense, black, earthy (melancholic) blood only, for Averroes assents that it does not cause fever unless it be mixed with phlegm, or red blood; therefore it does not form an imposthume, for the matter of both is the same.390 And Isaac says in the treatise he himself wrote on the urine, if an imposthume were formed of corrupt burnt humours turning to the nature of poison, such as formica, carbuncle, anthrax, and noli me tangere, it will be evil-smelling, with pain and itch, a blue black colour, corruption and mortification of the member.