De morborum temporibus, Principum Medicorum Aphorismoi

2. The order is of hours, or of days: irregularity is of both. Whence irregular fevers have no types.
3. The cause of this ἀταξία disorder is humor either changed into another, or transmitted in place of a humor.

XVIII.

Types are either permanent or mobile: the former invade and remit at the same hours, the latter at different ones.

XIX.

Mobile types are either προληπτικοί anticipatory or ὑστερικοί postponing: the former arrive earlier, the latter invade more slowly.
1. Anticipation, joined to the length of duration and vehemence of affliction, signifies increase.
2. Postponement, linked to the brevity and remission of the invasion, signifies decline.
3. A permanent type with equality of length and vehemence shows a state.
4. Commonly, they establish the cause of anticipation as the increase, attenuation, and movement of matter: the causes of postponement as the opposites of these. Fernel, book 4, chap. 11.
5. But the difference of humors, members, and remedies is also a cause.
6. For if the matter is regenerated more quickly, it anticipates: if more slowly, it postpones.
7. An accession that occurs through the transmission of a flow anticipates if the sense of the commanding member becomes more exquisite: if duller, it postpones.
8. An accession that occurs through the attraction of a flow anticipates if the pain or heat is increased: if it is remitted, it postpones.
9. An accession without a flow anticipates if the member becomes weaker: if stronger, it postpones.
10. An accession anticipates by remedies that increase heat or quantity: conversely, it postpones.
11. If none of these happens, the types are permanent.

XX.

Furthermore, types are either first or second: the former, if there is a short invasion and long remission: the latter, if the opposite.
1. The first are the tertian and quartan: the second, the quotidian and the highly extended semi-tertian.
2. The cause of a longer or shorter accession is the matter, the strength, and the habit of the body: reducing motion and rest to matter according to Avicenna: and exquisite or dull sense to strength.
3. Thick, viscous, cold, or copious matter is the cause of a longer accession: the opposites are the cause of a shorter one.
4. Weak strength causes a longer one: robust strength, a shorter one. The laxity of passages causes the former: constriction causes the latter.

Finally