Note that there are imposthumes both compound and simple, the latter from one humour only. Avicenna says: is the blood thick or thin? If it be thick, it forms an imposthume phlegmon, that affects the flesh and the skin together, accompanied by throbbing; if it be thin, it forms an imposthume that affects the skin only, without throbbing, and spina is its name. If it be formed from sanguine humour and choler, and sanguine humour be the stronger, there is