There are one or two objections to the mode of communication of cholera which I am endeavouring to establish, that deserve to be noticed. Messrs. Pearse and Marston state, in their account of the cases of cholera treated at the Newcastle Dispensary in 1853, that one of the dispensers drank by mistake some rice-water evacuation without any effect whatever.[[28]] In rejoinder to this negative incident, it may be remarked, that several conditions may be requisite to the communication of cholera with which we are as yet unacquainted. Certain conditions we know to be requisite to the communication of other diseases. Syphilis we know is only communicable in its primary stage, and vaccine lymph must be removed at a particular time to produce its proper effects. In the incident above mentioned, the large quantity of the evacuation taken might even prevent its action. It must be remembered that the effects of a morbid poison are never due to what first enters the system, but to the crop or progeny produced from this during a period of reproduction, termed the period of incubation; and if a whole sack of grain, or seed of any kind, were put into a hole in the ground, it is very doubtful whether any crop whatever would be produced.
EXPERIMENTS OF DR. THIERSCH ANSWERS TO CERTAIN OBJECTIONS.
Dr. Thiersch is of opinion, as appears by a discussion which has recently taken place at Munich, that the cholera evacuations are not at first capable of generating the disease; but that a decomposition takes place in them, and that in from six to nine days they become in a state to induce cholera. He founds this opinion on experiments which he performed by giving small quantities of the cholera evacuations to white mice. Although it is not contrary to all analogy that some change or development should take place in the cholera poison in the interval between its leaving one person and entering another, it is most probable that the fatal bowel complaint produced in white mice by Dr. Thiersch was not a specific disease, but the ordinary effect of putrifying ingesta. Many of the best attested instances of the communication of cholera are those, such as were related at the commencement of this work, where the patient is attacked in from twenty-four to forty-eight hours after first being near another patient, and although an interval of a week or so, often elapses between one case of the disease and those which follow, it is extremely probable that, in these instances, the evacuations remain the greater part of this time in a dry state on the soiled linen, without undergoing any change.
An objection that has repeatedly been made to the propagation of cholera through the medium of water, is, that every one who drinks of the water ought to have the disease at once. This objection arises from mistaking the department of science to which the communication of cholera belongs, and looking on it as a question of chemistry, instead of one of natural history, as it undoubtedly is. It cannot be supposed that a morbid poison, which has the property, under suitable circumstances, of reproducing its kind, should be capable of being diluted indefinitely in water, like a chemical salt; and therefore it is not to be presumed that the cholera poison would be equally diffused through every particle of the water. The eggs of the tape-worm must undoubtedly pass down the sewers into the Thames, but it by no means follows that everybody who drinks a glass of the water should swallow one of the eggs. As regards the morbid matter of cholera, many other circumstances, besides the quantity of it which is present in a river at different periods of the epidemic, must influence the chances of its being swallowed, such as its remaining in a butt or other vessel till it is decomposed or devoured by animalcules, or its merely settling to the bottom and remaining there. In the case of the pump-well in Broad Street, Golden Square, if the cholera poison was contained in the minute whitish flocculi, visible on close inspection to the naked eye, some persons might drink of the water without taking any, as they soon settled to the bottom of the vessel.
THEORIES OF THE CAUSE OF CHOLERA.
It is not necessary to oppose any other theories in order to establish the principles I am endeavouring to explain, for the field I have entered on was almost unoccupied. The best attempt at explaining the phenomena of cholera, which previously existed, was probably that which supposed that the disease was communicated by effluvia given off from the patient into the surrounding air, and inhaled by others into the lungs; but this view required its advocates to draw very largely on what is called predisposition, in order to account for the numbers who approach near to the patient without being affected, whilst others acquire the disease without any near approach. It also failed entirely to account for the sudden and violent outbreaks of the disease, such as that which occurred in the neighbourhood of Golden Square.
Another view having a certain number of advocates is, that cholera depends on an unknown something in the atmosphere which becomes localized, and has its effects increased by the gases given off from decomposing animal and vegetable matters. This hypothesis is, however, rendered impossible by the motion of the atmosphere, and, even in the absence of wind, by the laws which govern the diffusion of aeriform bodies; moreover, the connection between cholera and offensive effluvia is by no means such as to indicate cause and effect; even in London, as was before mentioned, many places where offensive effluvia are very abundant have been visited very lightly by cholera, whilst the comparatively open and cleanly districts of Kennington and Clapham have suffered severely. If inquiry were made, a far closer connection would be found to exist between offensive effluvia and the itch, than between these effluvia and cholera; yet as the cause of itch is well known, we are quite aware that this connection is not one of cause and effect.
Mr. John Lea, of Cincinnati, has advanced what he calls a geological theory of cholera.[[29]] He supposes that the cholera poison, which he believes to exist in the air about the sick, requires the existence of calcareous or magnesian salts in the drinking water to give it effect. This view is not consistent with what we know of cholera, but there are certain circumstances related by Mr. Lea which deserve attention. He says that, in the western districts of the United States, the cholera passed round the arenacious, and spent its fury on the calcareous regions; and that it attacked with deadly effect those who used the calcareous water, while it passed by those who used sandstone or soft water. He gives many instances of towns suffering severely when river water was used, whilst others, having only soft spring water or rain water, escaped almost entirely; and he states that there has been scarcely a case of cholera in families who used only rain water. The rivers, it is evident, might be contaminated with the evacuations, whilst it is equally evident that the rain water could not be so polluted. As regards sand and all sandstone formations, they are well known to have the effect of oxidizing and thus destroying organic matters; whilst the limestone might not have that effect, although I have no experience on that point. The connection which Mr. Lea has observed between cholera and the water is highly interesting, although it probably admits of a very different explanation from the one he has given.
DURATION OF CHOLERA IN DIFFERENT PLACES.
There are certain circumstances connected with the history of cholera which admit of a satisfactory explanation according to the principles explained above, and consequently tend to confirm those principles. The first point I shall notice, viz., the period of duration of the epidemic in different places, refers merely to the communicability of the disease, without regard to the mode of communication. The duration of cholera in a place is usually in a direct proportion to the number of the population. The disease remains but two or three weeks in a village, two or three months in a good-sized town, whilst in a great metropolis it often remains a whole year or longer. I find from an analysis which I made in 1849 of the valuable table of Dr. Wm. Merriman, of the cholera in England in 1832,[[30]] that fifty-two places are enumerated in which the disease continued less than fifty days, and that the average population of these places is 6,624. Forty-three places are likewise down in which the cholera lasted fifty days, but less than one hundred; the average population of these is 12,624. And there are, without including London, thirty-three places in which the epidemic continued one hundred days and upwards, the average population of which is 38,123; or if London be included, thirty-four places, with an average of 78,823. The following short table will show these figures in a more convenient form:—