A system of practical medicine. By American authors. Vol. 1

by Unknown

Influenza appears at all seasons of the year and affects the inhabitants of every latitude. It has no connection with known atmospheric conditions. Many of the earlier writers sought to establish a relation between low temperatures and sudden variations of temperature and influenza, and by reason of the confusion among the people between these diseases and common "colds" there has always existed an opinion that such a relation obtains. There is, however, no evidence to sustain this view; neither low temperature nor abrupt changes give rise to the affection. It has prevailed in hot and dry seasons, in the West Indies, on the coast of Java, in India, in Egypt, at the Cape of Good Hope, on the Riviera in summer.

The condition of the air as regards moisture, or dryness, does not influence the spread of the disease. It has occurred at sea, on low sea-coasts, and in the dryest climates, as, for example, in Upper Egypt.

Its spread is not much influenced by local winds. It does not travel with the same velocity, and even sometimes advances against them. In several well-authenticated instances a dense and foul fog has preceded and attended the local outbreak of epidemics. The much greater number of epidemics that have occurred altogether without such manifestations make it in a high degree probable that this has been a coincidence. Ozone in large quantities artificially produced may give rise to the symptoms of ordinary catarrh, but it is not a cause of influenza. The disease is not in any way connected with the condition of the soil, elevation, volcanic eruption, or any other local cause. The history of every epidemic may be adduced in proof of this statement.

Before taking up the consideration of the exciting causes of influenza, it is important to review the known facts concerning the march of epidemics and the spread of the disease in affected localities. It has prevailed with greater or less frequency in almost every region of the globe. Epidemics recur at irregular periods. It was at one time supposed that the course of the disease was cyclical, with a return at intervals of about one hundred years. This view was long ago proved to be unfounded. About every twenty-five or thirty-five years great epidemics have swept over vast areas of the globe, and influenza may be said to be, at such times, pandemic. Less-widely extended epidemics have taken place with greater or less frequency in the intervals between the great outbreaks. But it is not possible to establish anything like a regular periodicity in the returns of the disease.

It has been supposed in some instances to prevail within restricted localities, as, for example, in a single city. Such local epidemics are without doubt due to local causes, and are of the nature of simple ordinary catarrhal fever, rather than true influenza.

The epidemics have extended over great areas, usually in a direction from the east or north-east toward the west and south. At other times they take the opposite course, and in some years they have appeared to radiate in various directions from several centres. It is in consequence of these facts that two views have arisen concerning the origin of the affection. The first of these is, that each epidemic starts out from some single unknown source, and spreads thence from point to point, invading more distant localities successfully as it advances, until at length it dies out in regions remote from the starting-point. This opinion is in accord with the popular belief. Thus, the Italians have called it the German disease; the Germans, the Russian pest; the Russians, the Chinese catarrh. The geographical relation of these nations indicates the usual track of the great epidemics, as shown in the foregoing historical sketch. The other opinion is, that it arises not from some single particular place, but that it may start anywhere, and that widespread epidemics are due to the successive outbreaks of the disease at many distinct points of origin.

The evidence that the great epidemics of influenza are due to some general and pandemic influence is conclusive. The point of origin of the great epidemics has not yet been indicated with precision, and must remain beyond conjecture until further facts bearing upon the question of their source are brought to light. When it has prevailed over a large portion of the earth's surface its progress from place to place has usually been rapid. In this respect, however, the epidemics show a great diversity. It sometimes travels exceedingly slowly. It is said to have overrun Europe in six weeks, and it has again taken six months to do so. It sometimes attacks places widely remote from each other within short intervals of time, and it has appeared at the same time in different quarters of the globe. It does not follow the great lines of travel and commercial intercourse.

When influenza enters a city it continues to prevail, as a rule, from four weeks to two months, but exceptionally it remains a longer time; for example, the epidemic of 1831 was prevalent in Paris for the greater part of the year. It in all instances finally disappears, and sporadic cases do not occur in the intervals between the epidemics.

In rare instances the epidemics are heralded by scattered cases. But as a rule this disease attacks simultaneously great numbers of the inhabitants of affected districts, so that, when the epidemic is severe, the sick are in a short time to be counted by thousands and business is paralyzed as by a blow. Epidemics rapidly reach their height, and subside almost as suddenly as they began. In a large city the disease frequently, perhaps always, makes its appearance nearly at the same time in several different localities, affecting certain streets and quarters solely or more generally than others for a time, and spreading thus from several centres through the entire community. Large towns and cities are generally affected earlier than the villages around them, and the latter, though closely adjacent, sometimes escape for weeks. The crews of ships upon the high seas, not sailing from an infected port, are said to have suffered from the seizure, and epidemics have many times crossed the Atlantic from the Old World to the New, and more than once in the opposite direction.

2. The Exciting Cause.—Large as has been the place in medical literature occupied by the histories of epidemics of influenza, the nature of the "epidemic influence" which gives rise to the disease is still unknown.