Rhases mentions the critical days in the following terms: The 3d is critical in very acute fevers; the 4th is indicative of the 7th and 6th; the 5th is favorable; the 6th generally unfavorable; the 7th is a particularly favorable or unfavorable crisis; the 8th rarely critical, but if it be, unfavorable; the 11th critical and indicative of the 14th; the 12th rarely critical, and like the 8th; the 13th rarely critical; the 14th, critical and favorable; the 15th like the 13th; the 16th like the 12th; the 17th like the 9th, and indicative of the 20th; the 18th rarely critical, or unfavorable; the 19th rarely critical, or, if so, not bad; the 20th next to the 14th, and favorable; the 21st sometimes critical, but less frequently so than the 20th; the 24th resembling the 20th; after these the 27th, 31st, 37th, and 40th are critical. Averrhoes remarks, that great deference is due to Rhases’ opinion upon this subject, since it was confirmed by experience, in more than ten thousand cases, in an infirmary (in infirmaria Relenson). His list is very little different from that of Galen. In his ‘Continens,’ he gives an account of the system of Archigenes, but prefers that of Hippocrates. (xxxii.) Averrhoes states that the medical world was divided between the systems of Archigenes and Galen, but he inclines to the side of the latter in this case, although on most occasions given to dispute his authority. Avenzoar, upon the whole, nearly agrees with Rhases, but expresses himself undecided with regard to the 20th and 21st days. His authority must also be allowed to be of great weight upon this subject, if we may believe Averrhoes, that he lived to the age of one hundred and thirty-five, and practised medicine from his fortieth year. To the first class of critical days, according to Haly Abbas, belong the 7th and 14th; to the second, the 11th and 20th; to the third, the 4th, 17th, and 21st; and to the fourth, the 3d, 5th, 9th, and 18th. Alsaharavius gives a similar list to Haly’s. He inclines rather to the 20th than the 21st day. Galen, and most of the ancient authorities, believed that the critical days are influenced by the moon. Actuarius, in particular, attributes much to the influence of the sun and moon in influencing the course of fevers. Prosper Alpinus gives a correct summary of the ancient doctrines respecting the critical days. (De præs. Vita et Morte ægrot. vi, 4.) SECT. VIII.—THAT CRITICAL SYMPTOMS APPEARING IN THE COMMENCEMENT ARE UNFAVORABLE.