COMMENTARY. The Father of Medicine who was profoundly skilled in Semeiology, appears to have attached great importance to the observance of the critical days. At first, as Galen remarks, he seems to have been undecided respecting certain days, and, accordingly, he gives a somewhat different list of them in his ‘Prognostics’ and ‘Aphorisms,’ from what he has given in his ‘Epidemics.’ His latter list of critical days differs little or nothing from that of Galen. Galen reposes such confidence in the doctrine of critical days, that he affirms that, by a proper observance of them, the physician may be able to prognosticate the very hour when a fever will terminate. The following is his list: The 7th is particularly favorable; next, the 14th; next to these, the 9th, 11th, and 20th; then the 17th and 5th; afterwards the 4th, 3d, and 18th. The 6th is very doubtful and unfavorable; the 8th and 10th, like the 6th; the 12th, 16th, and 19th, like the 8th and 10th. Intermediate between these two lists of favorable and unfavorable days is the 13th. He informs us that Diocles and Archigenes held the 21st to be particularly favorable, but he agrees with Hippocrates in rejecting it and adopting the 20th. Celsus follows the system of Archigenes. He says, “κρίσιμοι dies erant, dies tertius, quintus, septimus, nonus, undecimus, quartus-decimus, unus et vicesimus; ita ut summa potentia septimo, deinde quarto-decimo, deinde uni et vicesimo daretur.” But he does not hesitate, afterwards, to express his distrust in the whole system; for, he adds, “verum in his quidem antiquos tunc celebres Pythagorici numeri fefellerunt; cum hic quoque medicus non numerare dies debeat, sed ipsas accessiones intueri.” The Greek writers subsequent to Galen adopt his system, with little or no alteration. Aëtius arranges the critical days thus: First in order, the 7th and 14th; then the 9th and 11th; next to them the 17th and 5th; then, the 4th; and afterwards the 3d and 20th. The 6th is usually bad. The last of the ancient authorities, Actuarius, is very full and confident in laying down the received doctrines, with regard to the critical days. He follows Galen. The Arabians, with scarce one exception, adopt the Galenic system. Avicenna, who treats of the critical days very fully, mentions the list of them given by Hippocrates and Galen, and also that by Archigenes, but decides in favour of the former.