This disease commences with feverish symptoms, shivering, followed by heat and dryness of the skin, a hard and frequent pulse, pain in the stomach, with nausea and vomiting and headache. Sometimes wild delirium, sometimes convulsions, attend its outset.

When Small-pox is fully formed, it cannot be mistaken for any other complaint; but it is of some importance to recognise it at its very commencement, for the severity of the impending disorder may sometimes be lessened by judicious measures adopted at that early stage. The symptoms, however, that mark the outset of all febrile diseases are necessarily very much the same. But, if the fever sets in when Small-pox is prevalent in the neighbourhood, if the person in whom it occurs is one who has neither had that disease nor been vaccinated, and especially if he be known to have been exposed, within from nine or ten days to a fortnight, to the Small-pox contagion, we may well suspect that the disease will turn out to be Small-pox, and act upon that suspicion.

When the pain in the back and vomiting are violent, they are usually followed by a severe form of the disease; the same may be expected from a continuance of the nausea and vomiting after the coming out of the eruption; which is very unusual. Heberden noticed that acute pain in the loins was almost always followed by a severe disorder; that pain higher up, between the shoulders, was a better symptom, and that it was always a good sign, if there was no pain in the back at all.

The eruption almost always begins to show itself on the third day of the fever. The earlier it comes, the severer generally does the disorder prove. The eruption usually comes out first on the face, then on the neck and wrists and on the trunk of the body; so that it does not cease to come out till the fifth day. Occasionally the spots appear first upon the extremities, but this is very rare. In some instances straggling pimples continue to spring up after the main crop is completed; but these stragglers seldom attain the same size as the others.

The pimples ripen gradually into pustules, and usually attain their height on the eighth day, and on that day they generally begin to break, and crusts or scabs to form. In four or five days more the scabs begin to fall off. In children, the crusts are sometimes visible on the seventh day; and in adults, when the disease is severe, they sometimes do not begin to form till the ninth day. The severity of the complaint is usually in proportion to the number of the pustules.

When the pustules are few in number they are separated from each other, and the Small-pox is then called distinct; when they are very many they run together, and the disease is then called confluent. The distinct form of the complaint is scarcely ever dangerous, and the confluent is seldom free from danger. During the time the pustules are filling up, the face swells, often to such a degree that the eyelids are closed. As the swelling of the face begins to subside, the hands and feet begin to swell.

On the eighth day of the eruption, or the eleventh day of the disease, a second accession of fever (called the fever of maturation) sets in. This secondary fever is very slight in the distinct Smallpox, but very intense and perilous in most cases of the confluent. It is at this period of the disorder that death, in the fatal cases oftenest occurs.

Both kinds are accompanied by sore throat; and sometimes in the distinct variety, and almost always in the confluent, a certain amount of salivation, which lasts for several days. At first the discharge is thin and plentiful, but afterwards it becomes thick and ropy, and the patient has some difficulty in getting rid of it.

When the scabs fall off, unless proper precautions have been taken, little hollows remain in the skin, and the patient is said to be pitted.

During the period of maturation, a peculiar greasy, disagreeable odour proceeds from the body of the patient, so that any one accustomed to the disease would know it at once by the smell. About the same time also many patients are tormented by itching of the skin, so that they are provoked to scratch off the heads of the pustules; and in this way they frequently cause pits. In many cases of confluent Small-pox, this itching seems to constitute the chief part of the patient's suffering.

Sir James E. Tennant states that the leopards (or panthers) in Ceylon are strongly attracted by the peculiar odour which accompanies Small-pox. The reluctance of the natives to submit themselves or their children to vaccination, exposes the island to frightful visitations of this disease; and in the villages in the interior it is usual on such occasions, to erect huts in the jungle to serve as temporary hospitals. Towards these the leopards are certain to be allured; and the medical officers are obliged to resort to increased precautions in consequence.

In the worst cases of this complaint the pustules, instead of being plump and yellow, are flat, red, purple, or blue; that is, they contain blood, or a sanious ichor in the place of pus, constituting what was called black Small-pox by Sydenham, and bloody Smallpox by Mead. These cases are usually fatal. Haemorrhage from the womb is not uncommon; and in pregnant women abortion, and then most commonly death. Occasionally the child in the womb takes the disease. In one case, related by Mr. Flinders, the disorder was eight or ten days later in the child than in the mother. A woman, near her full time, took Small-pox. The pustules were mature about the 10th or 11th of June. On the 18th she gave birth to a full-grown boy, upon whose face and body there were many pustules, distinct, and nearly ripe. The child died the same night. Sir William Watson describes an instance, in which the scars left by the pustules were visible upon an infant at its birth. This child was afterwards inoculated, without taking the disease. Its mother, who had formerly had it, nursed, when far advanced in pregnancy, a servant ill of Small-pox. Dr. Pearson met with a similar example. Mary Spooner was inoculated by him when six months pregnant, and had the disease severely. Her child was twice inoculated with Small-pox matter, but without effect.