EPIDEMIC. A contagious disease is so termed that attacks many people at the same season, and in the same place ; thus, putrid fever, plague, dysentery, &c. are often epidemic. Dr. James Sims observes, in the Memoirs of the Medical Society of London, that there are some grand classes of epidemics which prevail every year, and which are pro duced by the various changes of the sea sons. Thus, spring is accompanied by inflammatory diseases ; summer by com plaints in the stomach and bowels ; au tumn by catarrhs ; and winter by inter mittents. These being obviously pro duced by the state of weather attendant upon them, other epidemics are suppos ed analogous to them, and obedient to the same rules, which, on examination, not being the case, all further scrutiny is laid aside, perhaps too hastily.
The most natural and healthful seasons in this country are, a moderately frosty winter, showery spring, dry summer, and rainy autumn ; and whilst such prevail, the wet part of them is infested by vastly the greatest proportion of complaints, but those not of the most mortal kind. A long succession of wet seasons is accom panied by a prodigious number of diseases; but these being mild and tedious, the number of deaths are Niot in proportion to the co-existent ailments. On the other band, a dry season, in the beginning, is attended with extremely few complaints, the body and mind both seeming invigor ated by it ; if, however, this kind of weather last very long, towards the close of it a number of dangerous complaints spring up, which, as they are very short in their duration, the mortality is much greater than one would readily suppose, from the few persons that are ill at any one time : and as soon as a 'wet season succeeds a long dry one, a prodigious sickness and mortality come on univers ally. So long as this wet weather con tinues, the sickness scarcely abates, but the mortality diminishes rapidly ; so that in the last number of rainy years the number of deaths is at the minimum.
The change of a long dry season, whether hot or cold, to a rainy one, appears to bring about the temperature of air fa vourable to the production of great epi demics. Some, however, seem more speedily to succeed the predisposing state of the air, others less so ; or it may be, that the state of the air favourable to them exists at the very beginning of the change, whilst the state favourable to others progressively succeeds : of this last, however, Dr. Sims is very uncertain.
Two infectious diseases, it appears, are hardly ever prevalent together ; there fore, although the same distemperature of air seems favourable to most epidemic disorders, yet some must appear sooner, others later. From observation and books, the Doctor describes the order in which these disorders have a tendency to succeed each other to be, plague, pe techial fever, putrid sore throat, with or scarlatina, dysentery, small-pox, measl es, simple scarlatina, hooping-cough, and catarrh : "I do not mean by this," says he, "that they always succeed each other as above ; for often the individual infection is wanting, when another takes its place, until perhaps that infection is imported from a place, which has been so unfortunate as to have a co-incidence of the two causes, without which it ap pears that no epidemic can take place : that is, a favourable disposition of the air, and that particular infection. Whenever it happens that one infectious disorder takes the place that should have been more properly occupied by another, it becomes much move virulent than it is naturally, whilst the former, if it after wards succeeds, becomes milder in pro. portion : this, perhaps, is the reason why the same disorders, nay, the same ap pearance in a disorder, are attended with much more fatality in one year than another."