1. Infection, or “a peculiar matter generated in the body of a man in fever, which is carried by the atmosphere, and applied to some part of the body of a person in health, and which causes fever to take place in him.” That such a cause exists, he proves from observing that “of any number of men, one half of whom go near a person ill of a fever, and the other half do not, a greater number of the former will be infected, in a short period afterwards, than in those who do not.” He says he has known, in such circumstances, seven out of nine infected with the disease. This infection is not discoverable by smell or any other organ of sense; neither can the greatest attention to cleanliness disarm it of its malignity. Of this the Doctor says that he has known instances; nay, of a person going into a room where a feverish patient was, and bringing with him the infection, which was communicated to others in the room to which he came. He owns, however, that by allowing the air to stagnate in which feverish patients are, the infection will become extremely violent and fatal. This may naturally be supposed, even without having recourse to putrid effluvia; because, independent of these, the imperceptible infectious matter itself will undoubtedly be accumulated in the atmosphere of the room, and act more powerfully than it could have done had it been partly carried off and diluted by attention to cleanliness and ventilation. He also says, that “when a number of persons live in a small space, supposing even that they are kept as clean as possible, it happens frequently that fever arises in some, often in many of them. It has been in this case supposed, and is extremely probable, that some peculiar species of matter is produced, capable of producing fever, on being applied to the body.”
2. Effluvia from putrid animal or vegetable matters. Of this our author seems to be less fully ascertained than of the former, as he does not say that he has observed any instances of fevers arising from this cause; and he concludes by observing that “either the cause of fever, consisting of matter produced in the body of a person affected with this disease, seems probably different from that produced by putrefaction, or might be generated without any putrefaction taking place.”
3. Cold. Our author “is not disposed to allow that sudden exposure to cold occasions fever to take place, unless some symptom of the disease follows immediately. If a man had been suddenly exposed to cold, and continued in perfect health for twenty-four hours, the author would never allow that fever, or any other disease, was occasioned by it. In this case (exposure to cold) the evidence is much stronger than in that of infection; for the author (Dr. Fordyce) has seen many instances where, from exposure to cold, the commencement of the attack was instantaneous; and many are to be found in the records of medicine.”
4. Moisture. On this subject the Doctor observes, that the application of water to the body is not a cause of fever, unless the air has particles of water floating in it; in which case fever has ensued more frequently than in other cases. Water may exist in the atmosphere in three states. 1. In small drops suspended in it like dust in water. 2. In vapour. In this case the transparency of the air is not impaired, and a chemical combination, as it is called, between the air and water takes place. If the atmosphere be hot or dense, it is capable of combining chemically with a larger proportion of water. If therefore the atmosphere should in this manner be saturated with water, at any particular degree of heat or density, by diminishing either of these the vapour will be condensed, and the water reduced to the former state of suspension in small particles. 3. Water, heated to the boiling point, emits a steam, which combines chemically with the atmosphere, till the latter be saturated, after which it assumes the form of small particles; and this last is the only state which has been found to produce fever.
Moisture will also produce fever when applied to the body by wearing wet clothes. Those which imbibe or part with heat most slowly, are least apt to produce fevers on being heated. The warmer the atmosphere, the more liable people are to fevers from moisture.
It has been observed, that moisture from marshes, stagnating canals, or where the water runs very slowly, is more apt to produce fevers than what proceeds from the sea, lakes or rapid rivers. “This (says the Doctor) has given occasion to suppose that some other vapours proceed from such marshes beside water, and produce the disease. It certainly often happens, that a considerable degree of putrefaction takes place in marshy grounds, and more especially in warm climates; but it is by no means to be concluded that moisture in the atmosphere always produces fever in consequence of putrefaction. Putrefaction can only take place in vegetable or animal substances. If water therefore, not impregnated with either, should be in such a situation as to produce moisture in the atmosphere, no putrefaction can take place; therefore, if fevers ensue, they are certainly in consequence of moisture, not putrefaction. Many instances of this may be brought, as in the war which took place in Flanders, between the tenth and eleventh year of the present century, an army encamped upon sandy ground, in which water was found in digging less than a foot deep, and occasioned a great moisture in the air, which produced in a few days numbers of fevers, although the army was perfectly healthy before, and no more fevers were produced on shifting their ground. There are a vast many other instances of the same thing having taken place. Besides, fever has often arisen immediately in persons sitting in rooms, the floors of which had been just moistened with pure water.”
5. Certain kinds of food. On this Dr. Fordyce observes, that, though food of difficult digestion undoubtedly produces a number of diseases, he has never seen it productive of fever excepting once. Dr. Girtanner relates, that the emperor of Germany, having forced a number of his subjects to serve as soldiers, and sent them into an unwholsome part of Walachia, where he fed them with a kind of paste made of bread and water instead of meat, many of them died of the scurvy. The Doctor, however, does not ascribe this to any positive cause, but to three negatives, viz. the abstraction of the stimulus of nutriment, by feeding on the paste just mentioned; of the stimulus of oxygen in the corrupted atmosphere of Walachia; and lastly of the nervous stimulus, the most powerful of all; the greatest part being engaged by force against their will. This corroborates what Dr. Fordyce has said, that bad food is very seldom the cause of fever; for among so many, who used the imperial paste just mentioned, some would certainly have been affected by fevers, had it been capable of producing them; but, as it did not, it is most evident that the deficiency of stimuli is not the cause of fever.
6. Passions of the mind. These are looked upon by Dr. Fordyce to be among the less frequent causes of fever, though it is certain that they have been productive of multitudes of diseases, and even of sudden deaths; and Dr. Falconer, in his Prize Dissertation, ascribes to the passions very considerable effects in fevers, and even in the plague itself. “Contagious fevers (says he) afford strong instances of the influence of mental affections, both as prophylactics and remedies. The plague is a remarkable example, and the same reasoning extends to other disorders of a febrile, contagious nature. Fear, it is well observed by Dr. Cullen, by weakening the body, and thereby increasing its irritability, is one of the causes which, concurring with contagion, render it more certainly active, which he ascribes to its weakening effect on the body, by which its irritability is increased. Against this therefore he directs the mind to be particularly fortified, which is best done by giving people a favourable idea of the power of preservative means, and by destroying the opinion of the incurable nature of the disorder, by occupying the mind with business or labour, and by avoiding all objects of fear, as funerals, passing-bells, and any notice of the death of particular friends. Even charms might be used with good effect, could we promote a strong prepossession of their efficacy, either by the confidence they inspire, or by their engrossing the attention of the mind. It is no less certain, that a studious regard to promote hope and confidence in recovery, is equally necessary for the cure as for the prevention of such disorders. We know that contagious fevers have a peculiar tendency to diminish the energy of the brain, and of course to debilitate the whole system; and that this is especially the case with the plague, which produces the most considerable effects in weakening the nervous[82] system or moving powers, and in disposing the fluids to a general putrescency; and Dr. Cullen is of opinion that to these circumstances, as the proximate causes of the plague, regard should chiefly be had, both for the prevention and cure of this disorder. It must therefore be highly necessary, during the course of this disease, to attend to the support of the spirits, as on these the vital principles greatly depend; and they can by no means be so effectually kept up as by inspiring a confidence of recovery.”
Dr. Zimmerman presents us with a great number of examples of the influence of the passions in producing diseases, or death itself; some of the most remarkable of which follow. “All the passions (says he) when carried to excess, bring on very formidable diseases. Sometimes they occasion death, or bring us at least into imminent danger. The most reputable physicians agree in opinion that terror may occasion apoplexy, and death; and indeed they consider apoplexy as the most common effect of violent passion. Without being carried to excess, a passion will sometimes occasion a difficulty of breathing, together with a sense of stricture in the breast, and an hesitation to speak; the tongue remaining as it were immoveably fixed on the palate. Hysterical and hypocondriacal affections are sometimes the effects of grief in the most healthy people. Joy is much more dangerous to life than sudden grief. Sophocles died through joy at being crowned on account of a tragedy he had composed in his old age. The famous Fouquet died on being told that Louis XIV had restored him to liberty. The niece of the celebrated Leibnitz, not suspecting that a philosopher would hoard up treasure, died suddenly on finding under her uncle’s bed a box containing sixty thousand ducats. Violent anger has sometimes produced hæmorrhages and subcutaneous extravasations; or, some vessel of the brain being ruptured by these transports, a fatal apoplexy has taken place. There have been instances of excessive anger being succeeded by epilepsy, colic, or a violent degree of fever. Sometimes it has occasioned an increased flow of bile. In some this produces vomiting; in others it goes off downwards, and causes diarrhœa; or being retained, from a stricture of the gall-ducts, will perhaps be absorbed, and occasion jaundice. In cases where anger has been succeeded by extreme grief, obstructions have taken place in the liver. The effects of terror are similar to those of anger, but in general more violent. Sometimes excessive terror seems to give to men a preternatural strength, as is the case with madmen and drowning persons. In some cases it has not only excited immediate convulsions, but caused them to return periodically. Fear has been said to make the hair stand upright, and to contract the pores from which the hairs issue in the same manner as cold does. There are instances in authors even of the colour of the hair being changed by excessive fright. Philip V died suddenly on being told that the Spaniards had been defeated, and, on opening him, his heart was found ruptured. Timid people are more liable than others to fall sick. A firmness of mind is one of the best preservations against contagion. Willis has very well observed, that they who fear the small-pox the most are generally the first to be attacked with it. Cheyne assures us that fear is extremely prejudicial in all epidemical diseases. Dr. Rogers remarks, that fear constantly increases the ravages of a contagious disease. Rivinus attributed the propagation of the plague at Leipsic wholly to fear. The French physicians, who wrote on the plague at Marseilles, went so far as to deny its being contagious, and ascribed its propagation chiefly to fear.”
As for the cause of the plague itself, Dr. Fordyce supposes it to be produced by an infection of a particular kind. That which takes place in Syria and Egypt, he says, has only been clearly described by Dr. Russel; and it cannot be gathered from the accounts whether this may be originally produced without having been propagated as the first class of infections above mentioned are. “That disease (says he) called the plague, which ravaged this country (England) on considering the histories of the disease, seems to have been a fever,[83] produced by infections of the first class which have been enumerated.” Dr. Moore has given an account of the origin of a plague, which, if it could be depended upon, would decide the question concerning the origin of this dreadful distemper without previous infection. This passage is extracted from the History of the Royal Medical Society for the years 1777 and 1778. “Dr. Mitchell, physician to the hospital at Smyrna, appears, according to a memoir of which he is the author, sent by M. le Baron de Tott to the Medical Society to believe in the spontaneity of the plague (or that it arises of itself without any predisposing cause in the body) for proof of which he cites the following circumstance: A solitary shepherd, having no communication with any body, fell sick while he was tending his flocks; he went into an inhabited part, where he communicated the plague with which he found that he was attacked. This circumstance would prove much, if it was certain that the shepherd had no communication with others; if it were known how long, and with what precaution, he had been secluded from company: but the proofs of these are too difficult to be established to allow of any conclusion to be drawn from the fact. We are obliged therefore to acknowledge [it to be a doubtful matter] whether it is in fact a country that is the cradle of the plague; what country this is, supposing that such an one exists; or, finally, whether it sometimes appears spontaneously, and whether the first whom it attacks becomes the focus from whence it emanates.”