3. As different Liquors put upon a Ferment, are depurated in different times, so the Arterial Fluid takes up a determined Period, of which it is discharged of an induced Effervescence. 4. The Symptoms, during this Ebullition, do not proceed all along in the same Tenour; but on some days particularly, they give such evident Marks of their good or bad Quality, that the nature of the ensuing _Solution_ may very well be guess'd at, and foretold by 'em. Things being thus, Those days on which the Disease was so evidently terminated one way or other, might very justly be call'd the days of _Crisis_; and those upon which the tendency of Illness was discovered by most visible Tokens, the _Indices_ of the _Critical Days_. And thus far the Foundation was good, but when a false Theory happen'd unluckily to be joined to true Observations, this did a little puzzle the Cause. _Hippocrates_, it is plain, knew not to what to ascribe that remarkable regularity with which he saw the Periods of Feavers were ended on the _Seventh_, _Fourteenth_, _One and Twentieth_ day, _&c._ _Pythagoras_ his Philosophy was in those Ages very Famous, of which _Harmony_ and the _Mysteries of Numbers_ made a considerable part, _Odd_ were more Powerful than _Even_, and _Seven_ was the most perfect of all. Our great Physician espoused these Notions,[45] and confined the Stages of acute Distempers to a _Septenary_ Progression[46], upon which this Inconvenience follow'd, that when a Crisis fell out a day sooner or later than this Computation required, his Measures were quite broken; and that this must necessarily oftentimes happen, will appear by and by. Upon this score _Asclepiades_ rejected this whole Doctrine as vain,[47] and _Celsus_ finding it to be too nice and scrupulous, observes that the _Pythagorean Numbers led the Ancients into the Error_.[48] _Galen_ being aware of this, succeeded much better in his reasoning upon the Matter, and very happily imputed the Critical Changes not to the Power of Numbers, but to the Influence of the Moon; which he observes, _has a mighty Action upon our Earth, exceeding the other Planets, not in Energy, but in Nearness_[49]. So that according to him, the Septenary Periods in Diseases are owing to the _Quarterly Lunar Phases, which are the times of the greatest Force, and which return in about seven days_.[50]