8. Diarrhoea is always more or less prevalent in this country during the summer and autumn. There is no [{426}] reason to believe that epidemic diarrhoea is contagious, but there is a direct ratio between its prevalence and the temperature of the atmosphere and the absence of ozone. As the temperature rises the cases increase in number, and as it falls they diminish, and the disease is always most prevalent in very hot seasons. Diarrhoea may be due to many different causes, but its epidemic prevalence in autumn is chiefly accounted for by the absorption into the system of the products of putrefaction of organic matter, either in the form of gaseous effluvia or through the vehicle of drinking-water.
9. Typhoid or Enteric Fever is very commonly confounded with typhus, with which, however, so far as its origin is concerned, it has nothing in common. It is not, like typhus, confined to the poor, but it prevails among rich and poor alike; and, indeed, there are some reasons for believing that the rich and well-fed are more prone to be attacked by it than the destitute. It is the fever by which Count Cavonr, several members of the royal family of Portugal, and our own Prince Consort, came to their untimely end. It differs also from typhus in the circumstances that its origin and propagation are quite independent of overcrowding with defective ventilation, and are so intimately connected with bad drainage that by some physicians the fever is now designated pythogenic, or fever born of putridity. It is asserted by some writers that the poison of enteric fever is never generated in obstructed drains, but that the drains are merely the vehicle of transmission of the poison from an infected person. But if this were so, enteric fever must needs be a most contagious disease, whereas all experience goes to show that it rarely spreads, even under the most favorable circumstances. The disease, in fact, is so slightly contagious that many excellent observers have doubted if it be so at all. It is probable that certain meteorological conditions, such as a high temperature, a defective supply of ozone, or a peculiar electrical state, may be necessary for the production of the poison of enteric fever; and thus, nuisances which are offensive to the senses may exist for a long time without producing the disease. The necessity of a high temperature is undoubted, and is itself a strong alignment against the view which makes drains merely the vehicle of transmission of the poison. It is well known that enteric fever, like ordinary diarrhoea, becomes epidemic in this country every autumn, and almost disappears in spring, while the autumnal epidemics are always greatest in seasons remarkable for their high temperature. Enteric fever is much later in commencing and in attaining the acme of its autumnal prevalence than diarrhoea, showing that a longer duration of hot weather is necessary for its production; but, when once produced, a more protracted duration of cold weather seems necessary for its destruction.
10. Cholera. —Epidemic cholera is generally described as having originated at Jessore, in the delta of the Ganges, in the year 1817, and as having spread thence over Hindostan, and ultimately to Europe. Since 1817 Europe has been visited by three great epidemics of cholera, viz.: in 1832, in 1848-9, and in 1854; and at the present moment it is threatened with a fourth. During the past autumn the disease has appeared at Ancona and Marseilles, and at many other places in the basin of the Mediterranean. In England and Wales cholera destroyed 53,273 lives in 1849, and 20,097 in 1854. Although the great epidemics of cholera have appeared to take their origin in India, and gradually to have spread to Europe, following often the lines of human intercourse, the evidence in favor of its being a very contagious malady is small. The attendants on the sick are rarely attacked; and, on the other hand, the disease has often appeared in isolated localities, where it was impossible to believe that it was imported. It is a remarkable [{427}] circumstance, also, that some of the greatest epidemics which have occurred in India, as that of 1861, have shown no tendency to travel to Europe, notwithstanding the constant communication that exists. Even on the supposition, then, that cholera is of necessity imported from India, there must be something as yet unknown to us that favors its transmission at one time and not at another. But it is very doubtful if the disease is imported in the manner generally believed. Unequivocal cases of "Asiatic cholera" have been met with almost every year in the intervals of the great epidemics; and, as Dr. Farr has observed, it is highly probable that true cholera has always existed in England. The researches of the late Dr. Snow render it highly probable that the disease often arises from drinking water impregnated with the fermenting excreta of persons suffering from the disease; and if this be so, from what we know of other diseases, it is not unreasonable to infer that, in certain conditions of the atmosphere, the poison of cholera may be generated during the fermentation of the excreta of healthy persons. It can readily be conceived how the necessary meteorological conditions might originate in the East and gradually extend to this country, and thus lead to the supposition that the disease has been propagated by a specific poison.
11. Dysentery. —Epidemics of dysentery are confined to tropical countries, and need not occupy much attention at present. Atmospheric states which unduly or suddenly depress the temperature of the surface of the body are the most common exciting causes. They are most apt to take effect in the case of persons whose constitutions have been weakened by long exposure to extreme heat, to malaria, or to other debilitating causes. There is no positive evidence that dysentery is contagious.
12. Agues and Remittent Fevers are now but little known, and scarcely ever fatal, in this country. Many years ago, however, they were among the most common and the most fatal diseases of Britain. James I. and Oliver Cromwell both died of ague in London. The disappearance of ague has been in direct relation to the drainage and cultivation of the soil, and this remark applies not only to England, but to all parts of the globe. The fens of Lincolnshire and Cambridge are almost the only parts of England where agues arc now known; but in many countries, and particularly in the tropics, where the vegetation is very rank, they are still the most common of all diseases. Agues are not contagious, but result from the malaria given off during the evaporation from marshy uncultivated land. These malaria may be wafted to a considerable distance by the wind. A high temperature and rank vegetation seem to favor their production and to increase their virulence.
13. Influenza. —Severe and widespread epidemics of influenza have been observed in various parts of the world, from time immemorial. In the present century the disease has been epidemic in this country in 1803, 1831, 1833, 1837, and 1847. On each occasion it has been particularly fatal in aged and debilitated persons, and it has often been followed by an increased prevalence of other epidemic diseases. Influenza is not contagious, but depends on some unknown condition of the atmosphere. Sudden alternations of temperature have been thought to favor its origin.
14. The Sweating Sickness. —This remarkable and very fatal disease is happily now unknown in this country; but in the middle ages many great epidemics of it were observed, and nowhere were they more common than in England. Many of the epidemics were in fact confined to England. There are records of five distinct visitations of the disease during the fifteenth and sixteenth centuries, viz., in 1485, 1506, 1517, 1529, and 1551. The disease attacked all classes alike, and [{428}] was often fatal within a few hours. From the accounts handed down to us it is impossible to form any accurate idea as to the causes of its origin and extension; but the prevalent opinion at the time seems to have been that it was due in the first instance to atmospheric influences.
15. The Dancing Mania. —The present brief summary of the principal epidemic diseases would not be complete without alluding to the dancing mania of the fourteenth and fifteenth centuries. The effects of the Black Death of the fourteenth century had not yet subsided, and the graves of millions of its victims were scarcely closed, when we are told by Hecker a strange delusion arose in Germany, which took possession of the minds of men, and, in spite of the divinity of our nature, hurried away body and soul into the magic circle of the wildest superstition. It was a convulsion which in the most extraordinary manner infuriated the human frame, and excited the astonishment of contemporaries for more than two centuries, since which time it has never reappeared. It was called the dance of St. John or of St. Vitus, on account of the Bacchantic leaps by which it was characterized, and which gave to those affected, whist performing their wild dance, and screaming and foaming with fury, all the appearance of persons possessed. It was propagated by the sight of the sufferers, like a demoniacal epidemic, over the whole of Germany and the neighboring countries. While dancing, the infected persons were insensible to external impressions, but were haunted by visions, their fancies conjuring up spirits whose names they shrieked out. Some asserted that they felt as if immersed in a stream of blood, which obliged them to leap so high; while others saw the heavens open, and the Saviour enthroned with the Virgin Mary. The accounts of the dancing mania collected by Hecker at first sight seem almost fabulous, but cease to be so when we recollect the practices of certain modern religious sects and the accounts of the so-called "revivals" in the middle of the nineteenth century.
From the preceding summary, it is obvious that epidemic diseases vary greatly in their nature.
1. First we have diseases, such as small-pox, scarlet fever, and measles, which at the present day can only be traced to contagion, and some of which probably took their origin in the lower animals.