Hippocrates first established the doctrine of crisis and critical days, which were, the 3d, 5th, 7th, 9th, 1 1th, 14th, 17th, and 21st. Fevers were probably more regular in their periods at this time, because they were seldom interrupted in their progress by medicine. A crisis only respects acute diseases, and more particularly continual fevers. At this time, critical days are not a subject of frequent attention; the type of the disorder being changed, and the crisis accelerated or retarded, by what is administered.
Asclepiades and Celsus deny that diseases have their critical days; and Langius adds, "if a crisis is to be expected, medicine is superfluous."
The coincidence of critical days with the Pythagorean numbers, has induced many physicians to oppose the doctrine as fanciful, or to reject it as false. Others have as strenuously contended for the reality of changes generally salutary on particular days, rather than on others; and those particular days are the same which we have already mentioned.
There is little doubt of the universality of the tertian period. It has been proved by numerous facts, with great logical precision, by Stahl, in a separate dissertation. We generally find also a fever formed, not on the day following the action of the exciting cause, but on the alternate day. If the fever consists only of one paroxysm, the 3d or 5th will be salutary; if of two, the 7th. We thus find the first septenary period very clearly established. The 14th is generally acknowledged as a critical day; but the days of the interval are not so clearly established. The 11th is not strikingly critical; but if the patient pass the loth in safety, and the treatment be properly regulated, the disease generally terminates on the 14th. If in the evening of the 14th there is a violent fresh exacerbation, it is highly dangerous; yet a slight exacerbation is, in part, removed on the 17th, and completely on the 20th or 21st.
It will be obvious, that in the first fourteen days the crises observe the tertian period; afterwards the quartan; but the reason is uncertain, except that the constitution, accustomed to the action of the cause, is not so readily affected by it; for the more violent the cause, the shorter and the more violent are the periods, and the disease. In fact, we have been generally able, in this climate, to trace changes generally salutary on the days styled critical; and, if the practice is well conducted, they may be observed in almost every continued fever, though not in all equally striking.
De Haen, who acknowledges the influence of particular days, has taken the trouble of selecting the facts from the most approved works of Hippocrates; and of 163 instances of the termination of fever within the first twenty days, more than two-thirds, viz. 107, happened on the days mentioned as critical. None happened on the 2d or 13th; and upon the 8th, 10th, 12th, 15th, 16th, 18th, and 19th, there are but eighteen instances of termination. As, from the preceding facts, regular periods in fevers are sufficiently obvious, so from these the real periods appear to be those stated in the commencement of the article. De Haen Ratio Medendi, vol. i. p. 19.
The word crisis, however, is not confined to this signification; for sometimes it means the excretion of something noxious from the body, or of the noxious fluids in a fever; for the word signifies also to separate, or as it were to pass through a sieve.
Those who observe critical days consider crudity as that state of the morbid matter wherein it is unfit for a regular separation from the sounder juices; concoction, as that change in the morbid matter, by the power of nature, or assistance of art, which renders it fit for separation from the healthy part of our fluids; crisis is, therefore, the actual discharge of the morbid matter, whether brought on by the power of nature, or by medical aid; and the critical day is the time that this discharge happens. See Fedris.
On this subject see Hippocrates, Galen, P. AEgineta, Fernelius, De Haen, and Cullen; on the other side, Asclepiades, Celsus, Langius, Faber, and a tribe of moderns.