When the cold fit comes on every twenty-four hours, it is called a Quotidian; when there is a space of forty-eight hours between the attacks, it is called a Tertian; and when it appears on the first and fourth days, it is called a Quartan. That under the tertian type is most apt to prevail in the spring, and is the most common form of the disease. The quartan is the most obstinate and dangerous, being chiefly prevalent in autumn and winter. The quotidian is more likely than the others to assume the continued type.

The tertian Ague generally makes its attacks in the forenoon, the quartan in the afternoon, and the quotidian in the morning. The quartan, which has the longest intervals between the fits, has the longest and most violent cold stage, but, upon the whole, the shortest paroxysm. The hot fit of the tertian is comparatively the longest. The quotidian, with the shortest interval, has at the same time the longest paroxysm.

An Ague fit is composed of three distinct stages: the cold, the hot, and the sweating stage.

A person who it on the brink of a paroxysm of Ague, experiences a sensation of debility and distress about the region of the stomach; he becomes weak, languid, listless, and unequal to bodily or mental exertion. He begins to sigh, to yawn, and stretch himself; and soon he feels chilly, particularly in the back, along the course of the spine; he grows pale, his features shrink, and his skin gets dry and rough. Soon the slight sensation of cold, first felt creeping along the back, becomes more decided and more general: the patient feels very cold, and he acts and looks just as a man does who is exposed to intense cold, and subdued by it; he trembles and shivers all over; his teeth chatter, sometimes so violently that such as were loose have been shaken out; his knees knock together; his hair bristles slightly, from the constricted state of the skin of the scalp; his cheeks, lips, ears and nails turn blue; rings which before fitted closely to his fingers become loose; his breathing is quick and anxious; his pulse frequent sometimes, but feeble; and he complains of pains in his head, back, and loins; all the secretions are usually diminished; he may make water often, though generally he voids but little, and it is pale and watery; his bowels are confined, and his tongue is dry and white.

After this state of general distress has lasted for a certain time, it is succeeded by another of quite an opposite kind. The cold shivering begins to alternate with flushes of heat, which usually commence about the face and neck. By degrees the coldness ceases entirely, the skin recovers its natural colour and smoothness; the collapsed features and shrunken extremities resume their ordinary condition and bulk. But the reaction does not stop here; it goes beyond the healthy line. The face becomes red and turgid; the general surface hot, dry and pungent; the temples throb; a new kind of headache is felt; the pulse becomes full and strong, as well as rapid; the breathing is again deep, but oppressed; the urine is still scanty, but it is now high-coloured; the patient is exceedingly uncomfortable and restless. At length, another change comes over him: the skin, which from being pale andrough, had become hot and level but harsh, now recovers its natural softness; a moisture appears on the forehead and face; presently a copious and universal sweat breaks forth, with great relief to the feelings of the patient; the thirst ceases; the tongue becomes moist; the urine plentiful but turbid; the pulse regains its natural force and frequency; the pains depart; and by and by the sweating also terminates, and the patient is again as well, or nearly as well as ever.

The period that elapses between the termination of one paroxysm and the commencement of the next, is called an intermission; while the period that intervenes between the beginning of one paroxysm and the beginning of the next is called an interval. As the paroxysms are liable to vary in length, the intermissions may be very unequal, even when the intervals are the same. When the intermissions are perfect and complete, the patient resuming the appearance and sensations of health, the disorder is an intermittent fever. When the intermissions are imperfect, the patient remaining ill and feverish and uncomfortable in a less degree than during the paroxysm, then the complaint is said to be remittent fever.

Sometimes the paroxysm is incomplete: it is shorn of one or more of its stages; the heat and sweating occur without any previous shivering: or the patient shakes, but has no subsequent heat; or the sweating stage is the only one of the three that manifests itself. These fragments of a fit are often noticeable when the complaint is about to take its departure; but they may also occur at other periods of the disease. Sometimes there is no distinct stage at all; but the patient experiences frequent and irregular chills, is languid and uneasy, and depressed. This state is commonly known as the dumb ague or the dead ague.

A singular variety of Ague is recorded by Mr. Maugenet. In this case the usual order of the stages was reversed. "The patient upon each accession of the fit, was first attacked with profuse sweating, which lasted for an hour. Then the skin became dry and hot, and the face flushed, with headache, etc. This stage lasted ordinarily for five hours, when the patient began to feel cold, and eventually had distinct rigors." Quinine was as effectual in this remarkable variety, as in the regular forms of the disease.

Ague sometimes consists of a few paroxysms only, half a dozen, or four, or three, or even of one fit; or the fits may be protracted over a space of several weeks or months, or even years.

An ague may attack a person at any time; but they are much more common in spring, and in autumn, than in the other seasons of the year. The autumnal agues are the most severe and dangerous. The quotidian is most common in the spring; the quartan in the autumn; and the tertian is frequently met with both as a vernal and as an autumnal ague.