From the necessary influence of time, in thus rendering fevers of all kinds now and then contagious by excretion, it follows, that the yellow fever, when of its usual short duration, is incapable of generating that excretion, and that, instead of being considered as the only form of bilious fever that possesses a power of propagating itself, it should be considered as the only one that is devoid of it.
4. Miasmata, whether from marshes, or other external sources, acting upon a system previously impregnated with the excreted matters which produce the jail or ship fever. Mr. Lempriere informs us, that he saw what were supposed to be cases of yellow fever communicated by some sailors who brought the seeds of the ship fever with them to the island of Jamaica. The fevers which affected most of the crews of the Hussar frigate, mentioned by Dr. Trotter[29], and of the Busbridge Indiaman, described by Mr. Bryce[30], appear to have been the effect of the combined operation of foul air in those ships, and human excretions, upon their systems. The disease was barely tinged with bilious symptoms, and hence the facility with which it was cured, for the jail fever more readily yields to medicine than the yellow fever. The former was probably excited by some latent exhalation from dead matters in the holds of the ships, and hence we find it ceased on shore, where it was deprived of its exciting cause. It is true, great pains were taken to clean the hold and decks of the Busbridge, but there are foul matters which adhere to the timbers of ships, and which, according to Dr. Lind, are sometimes generated by those timbers when new, that are not to be destroyed by any of the common means employed for that purpose. Of this Dr. Kollock has furnished us with a most satisfactory proof, in his history of the yellow fever, which prevailed on board of the frigate General Greene, on her voyage to the Havanna, in the year 1799. “The air in the hold of the vessel (says the doctor) was so contaminated, as to extinguish lights immediately, and candles in the cockpit were almost as useless from the same cause. The fish were thrown overboard, and the decks washed and scoured, the ventilator and wind sails put in motion, and every measure of purification adopted that their situation allowed; notwithstanding these precautions disease invaded us. The men were unceasing in their exertions to purify the ship; washing, scouring with vinegar, burning powder and vinegar, old junk, and sulphur, added to constant ventilation, proved unequal even to the amelioration of their calamities, while they were in the latitude of great heat. After the removal of the sick, the ship was disburthened of her stores, ballast, &c. cleansed and white-washed throughout; still new cases occurred for nearly two months. Some days, two, three, or four were sent off to the hospital, which would seem to indicate the retention of some portion of this noxious principle, which was lodged beyond the reach of the cleansing process.” That this noxious principle or matter existed in the ship, and not in the bodies of the crew, is evident from its not having been communicated, in a single instance by a hundred of them who were sent to an hospital on Rhode-Island, notwithstanding an intercourse sufficient to propagate it was necessarily kept up with the inhabitants. Even their nurses did not take it[31].
5. A fifth instance in which contagion has been supposed to take place in the yellow fever is, where the exhalation from the excretions of a patient in that disease acts as an exciting cause, in persons previously impregnated with the marsh, or other external miasmata, which produce it. The activity of this exhalation, even when it is attended with no smell, is so great, as to induce sickness, head-ach, vertigo, and fainting. It is not peculiar to the exhalations from such patients to produce morbid effects upon persons who visit them. The odour emitted by persons in the confluent small-pox has been known to produce the same symptoms, together with a subsequent fever and apthous sore throat. This has been remarked long ago by Dr. Lind, and latterly by Dr. Willan, in his Reports of the Diseases of London[32]. That the yellow fever is often excited in this way, without the intervention of a supposed specific contagion, I infer from its sometimes spreading through whole families, who have breathed the same impure atmosphere with the person first infected by the fever. This is more especially the case where the impression made by the exhalation from the sick person is assisted by fear, fatigue, or anxiety of mind in other branches of the family. In favour of this mode of exciting the yellow fever, Dr. Otto communicated to me the following fact. In the autumn of the year 1798, it prevailed upon the shores of the Delaware, in Gloucester county, in New-Jersey. A mild remittent prevailed at the same time on the high grounds, a few miles from the river. During this time, the doctor observed, if a person who had inhaled the seeds of the yellow fever in Philadelphia afterwards came into a family near the river, the same disease appeared in several instances in one or more branches of that family; but where persons brought the fever from the city, and went into a family on the high grounds, where the mild remittents prevailed, there was not a single instance of a yellow fever being excited by them in any of its members. This fact is important, and of extensive application. It places the stimulus from the breath, or other exhalations of persons affected by the yellow fever, upon a footing with intemperance, fatigue, heat, and all the common exciting causes of the disease; none of which, it is well known, can produce it, except in persons who have previously inhaled the putrid miasmata, which in all countries are its only remote cause. The city of Philadelphia has furnished, in all our yellow fever years, many additional proofs of the correctness of Dr. Otto's remark. In the months of July and August, when miasmata are generally local, and float chiefly near to their hot beds, the docks and holds of ships, persons who are affected by these miasmata, and sicken in other parts of the city, never communicate the disease; but after the less prepared and heterogeneous filth of our whole city has been acted on by an autumnal, as well as summer sun, so as to emit pestilential exhalations into all our streets and alleys, the fever is now and then excited in the manner that has been mentioned, by a single person in a whole family. The common intermittents of the southern states are often excited in the same way, without being suspected of spreading by contagion. Even the jail or hospital fever is vindicated by Dr. Hunter from the highly contagious nature which has been ascribed to it, upon the same principle. His words, which are directly to my purpose, are as follow: “In considering the extent and power of the contagion [meaning of the jail or hospital fever], I am not inclined to impute to this cause the fevers of all those who are taken ill in one family after the first, as they are all along exposed to the same vitiated air which occasions the first fever. In like manner, when a poor woman visits some of her sick neighbours, and is taken ill herself, and afterwards some of her children, I would not impute the disease to infection alone; she and her family having previously lived in the same kind of vitiated air which originally produced the fever. If the cases in which the infection meets with the poison already half formed be excepted, the disease in itself will be found to be much less infectious than has been commonly supposed[33].” By the modes of communicating the yellow fever which have been admitted, the dysentery, and all the milder forms of autumnal fevers, have been occasionally propagated, and perhaps oftener than the first-named disease, from their being more apt to run on to the typhus or chronic state. Of this I could adduce many proofs, not only from books, but from my own observations; but none of these diseases spread by contagion, or become epidemic from that cause in any country. A contrary opinion, I know, is held by Dr. Cleghorn, and Dr. Clarke; but they have deceived themselves, as they formerly deceived me, by not attending to the difference between secreted contagions and morbid excretions from the body, produced by the causes which have been enumerated, and which are rare and accidental concomitants of bilious or summer diseases.
6. The last instance of supposed contagion of the yellow fever is said to arise from the effluvia of a putrid body that has died of that disease. The effluvia in this case act either as the putrified excretions mentioned under the first head, or as an exciting cause upon miasmata, previously received into the system. A dead body, in a state of putrefaction from any other disease, would produce, under the same circumstances of season and predisposition, the same kind and degrees of fever.
The similarity of the fever induced by the means that have been enumerated, with the fever from which it was derived, has been supposed to favour the opinion of its being communicated by a specific contagion. But let it be recollected that the yellow fever is, at the time of its being supposed to be thus received, the reigning epidemic, and that irritants of all kinds necessarily produce that disease. The morbid sweats which now and then produce an intermitting fever, and the alvine excretions which occasionally produce a dysentery, act only by exciting morbid actions in the system, which conform in their symptoms to an immutable and universal law of epidemics. It is only when those two diseases generally prevail, that they seem to produce each other.
Thus have I explained all the supposed cases of contagion of the yellow fever. To infer from the solitary instances of it thus excited, is to reason as incorrectly as to say the small-pox is not contagious, because we now and then meet with persons who cannot be infected by it.
From the explanation that has been given of the instances of supposed contagion of the yellow fever, we are compelled to resort to certain noxious qualities in the atmosphere, as the exclusive causes of the prevalence, not only of that fever, but (with a few exceptions) of all other epidemic diseases. It is true, we are as yet ignorant of the precise nature of those qualities in the air which produce epidemics; but their effects are as certainly felt by the human body as the effects of heat, and yet who knows the nature of that great and universal principle of activity in our globe?
That the yellow fever is propagated by means of an impure atmosphere, at all times, and in all places, I infer from the following facts: