This sickness is also778 caused by sanguine humour or choler, or melancholy; but most often by phlegm, mixed with choler,779 for otherwise it would not penetrate well. Then, it is also caused by crude humours, and then by choler, rarely by melancholy, the which by reason of its paucity, compared with the other humours, cannot penetrate to the joints because of its hardness, nor to the passages approaching them because of its grossness.