The first of these is produced by six causes. First, the strength of the member that expels the matter, for Galen says, the strong members send their excess to the weak members, and the noble members to the ignoble. Second, the weakness of the evacuatory force in the member that receives the matter. Third, the quantity of the matter. Fourth, the width of the pores. Fifth, the want of nutritive force and power of360 conversion in the member, to which the matter has been sent. Sixth, that the members361 which receive the matter are subject to the members that put it from them. Constantine puts these causes
p.169in the eighth book of Pantechnes, and362 these two further causes may be added to them:namely, the movement of the member to which the matter is sent, and its heat. 363 For Galen says, it is easier to pour the matter to a member that moves and heats, than to other members; therefore the imposthumes that move and are caused by crisis are oftener formed in the joints, than in other places, because of the amount of movement and space therein.