Section Iii.--Causes--Propagation.

The remote or final cause is essentially of miasmatic origin, developed under certain atmospheric and terrestrial local conditions, not well defined or fully understood. In its nature and essence, it constitutes a peculiar disease-poison, which is now generally admitted to be, in one way or another, absorbed, and infects the blood, inducing a primary disease of this vital fluid, and directly depressing and deranging the ganglionic system of nerves. To its general character, and the circumstances under which it is generated and in which it operates in producing the disease, we have alluded in speaking of its origin.

The predisposing causes are as numerous as the varied influences which operate to depress the general health. The insalubrity of the atmosphere may be regarded as a general, and, perhaps, the most extensive predisposing cause. In this state, its vital element becomes diminished or impaired to such an extent as to render it incapable of sustaining the normal and healthy functions of the system in their most vigorous condition. Hence, the foul and noisome air of close, ill-ventilated apartments becomes very depressing and baneful; a direct and effective element, often, in constant operation in generating and producing the cholera, typhoid fever, or other deadly maladies. This is not unfrequently the case on board some of our emigrant ships, when hundreds of human beings are stowed away between decks without the means of efficient ventilation, disinfection, or other mode of expelling the noxious principle. Though the germ of disease may be ever on board, it does not vegetate and come forth and rapidly acquire its activity, vigor and power, unless the localizing influence vivify, foster and nurture its development. This is fully confirmed by the recent arrival of two steamers with cholera on board.

The England, and a few days later the Virginia, with crews and passengers all in perfect health, departing from a healthy port where no cases of cholera were known to exist, and after being out at sea six or eight days under the influence of a cool, invigorating atmosphere, were surprised by the sudden irruption of cholera on board. It breaks out among the steerage passengers who are crowded and packed together between decks like sheep for the slaughter, in a confined atmosphere, daily becoming more noisome, without the means of ventilation or disinfection. Can any sane man say the disease--the cholera--was not here, on board these ships, generated and produced?

This is also confirmed by the occurrence of an isolated case on Ninety-third Street, near Third Avenue, the first case in this city this season. Though the cholera exists at Quarantine, the patient had not been in any way exposed to the disease, except to the exhalations from the overflowing and drainage of a privy and the foul atmosphere arising from the cellar of her own tenement. On Monday, it is said, she partook of her dinner, feeling a little indisposed; at 4 P.M. she called in her physician, and died the next morning, May 1st, at 11 A.M., in a state of collapse.

Take another instance: the second case in this city occurred in one of the tenement dwellings of the Sixth Ward, No. 117 Mulberry Street. The patient was a woman about thirty years of age, who had not been exposed, except to the noisome atmosphere of her own dwelling and its surroundings, which must be regarded, under the peculiar circumstances, as a true, genuine cholera atmosphere. In these cases the evidence is conclusive that the disease was generated and produced within, and on these premises.

The exhalations from low, moist, and marshy localities, from the offensive cesspools, water-closets, sinks, sewers, and the decomposition of animal and vegetable substances, from the refuse or garbage which so often befouls the sidewalks and gutters of streets, are all effective, predisposing causes, that directly facilitate the production of the cholera. Whatever tends to depress the vital powers, impair normal action, or relax in any degree the tone of the nervous system, favors the operation of the final cause. So, too, the low, underground, damp, unventilated apartments, the crowded and uncleanly tenement houses, in which multitudes of the poorer class live, in a confined, foul, and noisome atmosphere, not only favor, but actually invite, the active operation of the infecting agent.

Habits of intemperance, profligacy, impurity, and late hours, have a powerful influence to depress and prepare the system for an invasion of the disease in its most malignant form. In a neighborhood of this description, when the cholera in 1832 was raging in the adjacent city, from which it was separated by a very small creek, the uncleanly multitude escaped entirely, not a case occurring there at that time; but when, after an interval of several weeks, all danger seemed to have passed, and the people were rejoicing and congratulating themselves on their good fortune, the fearful disease suddenly appeared in their midst with greatly intensified effect, and in a very few days swept the place so clean that few were left to tell the sad story of its ravages.

There are some other predisposing causes of no inconsiderable influence, which not only favor the operation of the infecting agent in the production of the disease, but even awaken its latent power, and stimulate its activity and development in the system, once exposed to its invasion. Among these, excessive fear of an attack, great anxiety and depression of mind, constitutional debility, deranged condition of the digestive organs, accompanied with a relaxed state of the bowels, exhaustion arising from fatigue or disease, semi-starvation and unwholesome diet, neglect of personal and domestic cleanliness, irregular habits, and excesses of every description, are all direct incentives and stimulating agents in the production of the cholera. Any one of these may be sufficient to induce an attack; but when a number unite and act conjointly the danger is vastly greater, as the infecting agent or disease-poison becomes thereby more intensified.

When the cholera first appeared in Europe and in this country in its epidemic form, the majority of medical men, as well as the people, believed it to be contagious, and to be propagated solely on this principle. But when the disease appeared in 1848 a decided change of opinion occurred, which led to a full discussion of the subject, without any definite result; and the great question as to its contagious character and its mode of propagation remains still unsettled. The higher authorities, says an eminent author, concurred in the opinion of the Board of Health, "that the disease was not in any way contagious, and that no danger was incurred by attendance on the sick."

A large body of evidence, however, has been exhibited, going to show that human intercourse has, at least, a share in the propagation of the disease, and that it, under some circumstances, is the most important, if not the sole means of effecting its diffusion. On the other hand, it is affirmed that though it may be communicated, in some cases, by the agency of human intercourse, it does not follow that the material cause spreads by true contagion, that is, by reproducing itself in the bodies of men, and there only.

The disease may be carried by healthy persons in their clothing, in their ships, and in their caravans. That instances of this kind have occurred there can be no question, for numerous records present some undoubted instances of the occasional communication of the cholera-poison through human intercourse; still it is no less certain that its general extension over the world cannot be accounted for on this principle alone. "Its propagation by this means seems to be the rare exception, its spread over the earth from other causes being the common rule."

Dr. Hamlin, writing from Constantinople, in reference to the recent irruption and prevalence of the cholera in that city, observes, "The idea of contagion should be abandoned. All the missionaries who have been most with the most malignant cases, day after day, are fully convinced of the non-contagiousness of the cholera. The incipient attacks which all have suffered from are to be attributed to great fatigue, making the constitution liable to an attack."

It is a very singular fact, that the medical profession in India, the birthplace and home of the cholera, almost universally reject the doctrine of contagion. If those most observant and familiar with its history, its prevalence, and its annual recurrence as an endemic disease, which they are called to treat in all its varied phases, have discovered no contagious character by which it can be propagated, it may be safely inferred that it is not contagious in the common acceptation of the term, and that its extension over the earth is governed by some other principle, and that the predisposing and localized causes which are always in operation in India exercise no small share in its diffusion, in directing its course, aggravating its severity, increasing or diminishing its fatality, and determining the duration of its prevalence in particular localities. When its infecting germs have gained a lodgment in any city, section, or country, they may be stimulated and become exceedingly active in the production of the disease through these influences.

As to its introduction into different countries, it is quite evident that the germ, or latent principle of the cholera-poison, exists in such a state as to be capable of transportation, and may in this way be diffused to almost any extent when the localizing influences are sufficient to develop its energies.

In this, as in all other zymotic diseases, some persons are more susceptible of an impression and more liable to an attack than others. Though no class can be considered exempt, yet there are some whose organization, or innate protective principle, seems to render them impervious to its influence. The cholera, however, is no respecter of persons, or rank, or condition. The anæmic and cowardly in all ranks and conditions are peculiarly liable, and are the most defenceless and unresisting when invaded. In Europe, the probable numbers attacked in that part of the world appear from statistics to be, in France, as 1 in 300; Russia, as 1 in 20; Austria, as 1 in 30; Poland, as 1 in 32; Holland, as 1 in 144; Germany, as 1 in 700. "The circumstance of one attack by no means protected the individual from a second in the same, or any subsequent year; still a repetition of the disease in the same person in the same year was rare."