Sec. 249. The Cause of Malignant Fevers is, not infrequently, combined with other Diseases, whose Danger it extremely increases. It is blended for Instance, with the Poison of the Small-Pocks, or of the Measles. This may be known by the Union of those Symptoms, which carry the Marks of Malignity, with the Symptoms of the other Diseases. Such combined Cases are extremely dangerous; they demand the utmost Attention of the Physician; nor is it possible to prescribe their exact Treatment here; since it consists in general of a Mixture of the Treatment of each Disease; though the Malignity commonly demands the greatest Attention. __Chapter XVIII.__ _Of intermitting Fevers._ __Sect.__ 250. Intermitting Fevers, commonly called here, Fevers and Agues, are those, which after an Invasion and Continuance for some Hours, abate very perceivably, as well as all the Symptoms attending them, and then entirely cease; nevertheless, not without some periodical or stated Return of them. They were very frequent with us some Years since; and indeed might even be called epidemical: but for the five or six last Years, they have been much less frequent throughout the greater Part of _Swisserland_: notwithstanding they still continue in no small Number in all Places, where the Inhabitants breathe the Air that prevails in all the marshy Borders of the _Rhone_, and in some other Situations that are exposed to much the same humid Air and Exhalations. Sec. 251. There are several Kinds of intermitting Fevers, which take their different Names from the Interval or different Space of Time, in which the Fits return. If the Paroxysm or Fit returns every Day, it is either a true Quotidian, or a double Tertian Fever: The first of these may be distinguished from the last by this Circumstance, that in the Quotidian, or one Day Fever, the Fits are long; and correspond pretty regularly to each other in Degree and Duration. This however is less frequent in _Swisserland_. In the double Tertian, the Fits are shorter, and one is alternately light, and the other more severe. In the simple Tertian, or third Day's Fever, the Fits return every other Day; so that three Days include one Paroxysm, and the Return of another. In a Quartan, the Fit returns every fourth Day, including the Day of the first and that of the second Attack: so that the Patient enjoys two clear Days between the two sick ones. The other kinds of Intermittents are much rarer. I have seen however one true Quintan, or fifth Day Ague, the Patient having three clear Days between two Fits; and one regularly weekly Ague, as it may be called, the Visitation of every Return happening every Sunday.