The time of digestion; moreover for only when the matter is digested is it proper to administer the medicine to purge the particular humor, just as Hippocrates says, ‘Digesta medicare, et cetera.’ For that reason Avicenna says that there are two things which assist the operation of the medicine, i.e. digestion of the matter, and openness of the passages. The season of the year also since Avicenna says that it is proper to observe it as an adjuvant to purging; because at the time when the constellation called canis major is rising such as is visible in the summer, or at the time of severe cold such as the winter, laxatives are not suitable to take. For that reason Hippocrates says; ‘Sub Cane et ante canem, et cetera.’ The medicine is suitable, however, to administer in the spring and autumn. Yet, should purging be necessary, and the constitutional vigor (of the patient) be good, hindrance by anything is not to be considered. For that reason it is possible to cause purging in the summer and in the winter. That is properly done, however, with mild medicines such as cassia fistola, manna, and tamarinds.