4 Le Cholera, 1883.
ETIOLOGY.—The essential cause of cholera is unknown, unless the investigations of Koch, described below, may have revealed it. Its secondary causes, or the conditions of its dissemination, are better understood. Some general propositions concerning them will here be laid down, and illustrated so far as the argument requires and the available space will allow.
Cholera is endemic in no other country than India, and more particularly in Bengal. When it has occurred elsewhere it has invariably been carried from India. The cholera poison has been imagined to be of an aërial nature, but its diffusion has no relation whatever to the velocity or the direction of the wind. In no instance whatever has its rate of progress exceeded that of man on land or water, nor has it ever taken a direction different from that of commercial or military movements. On land it has usually crept from place to place, and if sometimes it has seemed to leap across wide spaces, and even seas and oceans, it has never invaded any inland town or seaport without having been brought thither from a point already affected with the disease. Nor, having once entered an inland or seaboard town, does it spread equally therein in all directions, but prevails chiefly in the quarter immediately surrounding the place of its entrance. If appropriate sanitary measures are enforced, it is sometimes confined to that quarter, and, in the case of quarantine stations, it has repeatedly been prevented from extending beyond them. This statement may be illustrated by the fact that of fourteen epidemics of cholera at Staten Island, the quarantine station of New York, all but four were prevented from reaching that city.5 When the disease does overleap the barrier opposed to it, its origin and subsequent course can usually be traced.
5 Peters's Notes, etc., 2d ed., p. 94.
A high atmospheric temperature is everywhere associated with the prevalence of cholera. Its origin in the hot climate of Hindostan and its general progress prove this conclusively. In nearly all of the places where a great difference exists between the summer and the winter temperature the disease has disappeared during the cold season, and attained its greatest intensity during the hot months of the year. The only apparent exception to this rule is, that cholera has prevailed in several Russian, Swedish, and Norwegian cities during the winter. But these very exceptions confirm the rule; for in the countries mentioned the intense cold of the winter compels the inhabitants to seal their houses by every possible means, while the atmosphere within them is kept at a high temperature by huge stoves, which hinder ventilation, and indeed render it almost impossible. Difference of temperature likewise explains the fact that of two cholera-ships arriving from Havre, the one at New York and the other at New Orleans, in December, 1848, the former did not disseminate the disease, but the latter formed the starting-point of an epidemic which lasted all the winter.
A good deal has been written of the predisposing causes of cholera, and poverty, crowding, filth, intemperance, and depression of spirits have been given prominent places in the catalogue. But to any one familiar with the history of epidemic diseases it will at once be apparent that every one of these conditions favors the spread of all communicable infectious diseases. There is not the slightest evidence that these agencies, singly or combined, can generate cholera or favor its spread apart from the presence of the specific poison of the disease and the facility with which it is transmitted from the sick to the well whenever the population is crowded, poor, of filthy habits, and weakened by dissipation. Because among such people intemperance prevails, this vice has been regarded as predisposing to cholera. Apart from the brutish mode of living of drunkards, there is nothing to show that they are more liable to cholera than the most abstemious of water-drinkers. On the contrary, it is notorious that during cholera epidemics drunkards in the better classes of society enjoy a certain degree of immunity from the disease; which it is easy to explain on the ground that they imbibe but little water, which is the main channel through which the infectious principle of the disease is spread.
The specific cause of cholera is taken into the alimentary canal, and acts through it to produce the characteristic symptoms of the disease. It is conveyed from the sick to the well by means of the gastro-intestinal discharges, either moist or dry; in the former state, by means of drinking-water, and in the latter through the air, whose suspended noxious particles are received into the fauces and swallowed. There is reason to believe that the poison does not enter the system through the lungs, or through any other channel than the gastro-intestinal canal. W. B. Carpenter6 appears to hold, however, that the poison may be absorbed through the lungs. To this view there are two objections: 1, That whatever is taken into the mouth or throat by inspiration may very well be swallowed; and, 2, that all the primary lesions of cholera affect the digestive and not the respiratory apparatus. It is not at all necessary to the propagation of cholera that its excreta should be furnished by persons laboring under the fully-formed disease. A specific choleraic diarrhoea is as infectious as the evacuations which occur in completely developed cholera. But neither will propagate the disease through the air to a distance. The tendency to its propagation in this manner depends chiefly upon the concentration of the poison; thus, it much more frequently occurs in close than in well-ventilated rooms or than in the open air. It has been argued that cholera is not contagious, because so few, comparatively, of the attendants upon cholera patients contract the disease. On the other hand, as some of them are attacked, this positive fact outweighs an indefinite number of negative instances. It should also be noted that different diseases enter the system and infect it through different channels—some through the lungs, others through the alimentary canal, etc. Small-pox, the most contagious of all diseases, is introduced through the air-passages, and is probably harmless when its virus is taken into the stomach. That the converse of this proposition applies to cholera is sustained by the whole history of the disease. Cholera poison may be taken to considerable distances in either a moist or a dry condition. In the former state it is mainly conveyed by water, as in rivers, water-pipes, etc.; in the latter, by fomites and especially by clothing saturated or merely soiled with cholera discharges, and which may retain their infectious quality for an indefinite time.
6 The Nineteenth Century, Feb., 1884.
Great stress has been laid upon the humidity and foulness of the soil, a damp atmosphere, filth, crowding, etc., as elements in the production of cholera, but in reality they have no more essential relation to it than to any other disease that occurs epidemically. Cholera may prevail whether they are present or absent. It is evident that from the earliest historical periods all of these causes of disease have existed, and in Europe much more generally and excessively than during the present century, and that they have never been removed in Asia Minor, Egypt, Arabia, and Africa. Yet cholera never was known in any of these countries until it was brought into them about the end of the first third of the present century.
According to Pettenkoffer, cholera is most prevalent when the subsoil water is lowest, and least so when the subsoil water is highest. It would be more descriptive of the fact to say that, so far as cholera has anything to do with the condition of the soil, it is most apt to be severe and prevalent when very dry weather follows a very wet period. Such circumstances are the most favorable to putrefactive fermentation and the dissemination of its products, which thus reach wells of drinking-water, and even rivers, especially when sewers empty into the latter. The identity of this explanation with that which is generally accepted for the dissemination of typhoid fever is too evident to be insisted upon. We might go farther, and say that, in typhoid fever as in cholera, the disease is communicated, although exceptionally, by the air of the sick room and by the exhalations of the soiled fomites of the patient. Now, if typhoid fever resembled cholera not only in being transmitted by means of the dejections, but also in its poison being derived from one primary source only, the analogy between the causes of the two diseases would be very striking indeed. But, in point of fact, the typhoid-fever poison may probably be generated de novo by fecal fermentation and other forms of putrefaction, and the disease is only exceptionally communicable; whereas, the poison of cholera, once received, is conveyed from man to man and far and wide through various channels; but, so far as is known, it has but one primary source, and that is in India. Lebert states that he did not find the localities that are the ordinary seats of typhoid fever peculiarly liable to invasions of cholera. But it must be noted that typhoid fever is very far from being exclusively a disease of the poor, squalid, and vicious. Like death itself, "regum turres pauperumque tabernas æquo pede pulsat;" while cholera much more commonly plants itself and disseminates its seeds in the rank soil of moral and physical degradation.