It has been asked, if the yellow fever be not imported, why does it make its first appearance among sailors, and near the docks and wharves of our cities? I answer, this is far from being true. The disease has as often appeared first at a distance from the shores of our cities as near them, but, from its connection with a ship not being discovered, it has been called by another name. But where the first cases of it occur in sailors, I believe the seeds of it are always previously received by them from our filthy docks and wharves, or from the foul air which is discharged with the cargoes of the ships in which they have arrived, which seeds are readily excited in them by hard labour, or intemperance, so as to produce the disease. That this is the case, is further evident from its appearing in them, only in those months in which the bilious fever prevails in our cities.
It has been asked further, why were not these bilious malignant fevers more common before the years 1791, 1792, and 1793? To this I answer, by repeating what was mentioned in another place[37], that our climate has been gradually undergoing a change. The summers are more alternated by hot and cool, and wet and dry weather, than in former years. The winters are likewise less uniformly cold. Grass is two or three weeks later in the spring in affording pasture to cattle than it was within the memory of many thousand people. Above all, the summer has encroached upon the autumn, and hence the frequent accounts we read in our newspapers of trees blossoming, of full grown strawberries and raspberries being gathered, and of cherries and apples, of a considerable size, being seen, in the months of October and November, in all the middle states. By means of this protraction of the heat of summer, more time is given for the generation of putrid exhalations, and possibly for their greater concentration and activity in producing malignant bilious diseases.
It has been asked again, why do not the putrid matters which produce the yellow fever in some years produce it every year? This question might be answered by asking two others. 1st. Why, if the yellow fever be derived from the West-Indies, was it not imported every year before 1791, and before the existence, or during the feeble and partial operation of quarantine laws? It is no answer to this question to say, that a war is necessary to generate the disease in the islands, for it exists in some of them at all times, and the seasons of its prevalence in our cities have, in many instances, had no connection with war, nor with the presence of European armies in those and in other sickly parts of the globe. During the seven years revolutionary war it was unknown as an epidemic in the United States, and yet sailors arrived in all our cities daily from sickly islands, in small and crowded vessels, and sometimes covered with the rags they had worn in the yellow fever, in British hospitals and jails. I ask, 2dly, why does the dysentery (which is certainly a domestic disease) rise up in our country, and spread sickness and death through whole families and villages, and disappear from the same places for fifteen or twenty years afterwards?
The want of uniformity in the exhalations of our country in producing those diseases depends upon their being combined with more or less heat or moisture; upon the surface of the earth being completely dry, or completely covered with water[38]; upon different currents of winds, or the total absence of wind; upon the disproportion of the temperature of the air in the day and night; upon the quantity of dew; upon the early or late appearance of warm or cold weather; and upon the predisposition of the body to disease, derived from the quality of the aliments of the season. A similar want of uniformity in the annual operations of our climate appears in the size and quality of grain, fruits, and vegetables of all kinds.
But the greater violence and mortality of our bilious fevers, than in former years, must be sought for chiefly in an inflammatory or malignant constitution of the atmosphere, the effects of which have been no less obvious upon the small-pox, measles, and the intercurrent fevers of Dr. Sydenham, than they are upon the summer and autumnal disease that has been mentioned.
This malignant state of the air has been noticed, under different names, by all the writers upon epidemics, from Hippocrates down to the present day. It was ascribed, by the venerable father of physic, to a “divine something” in the atmosphere. Dr. Sydenham, whose works abound with references to it, supposes it to be derived from a mineral exhalation from the bowels of the earth. From numerous other testimonies of a belief in the influence of the insensible qualities of the air, altering the character of epidemics, I shall select the following:
“It is certain (says Dr. Mosely) that diseases undergo changes and revolutions. Some continue for a succession of years, and vanish when they have exhausted the temporary, but secret cause which produced them. Others have appeared and disappeared suddenly; and others have their periodical returns.”
The doctor ascribes a malignant fever among the dogs in Jamaica (improperly called, from one of its symptoms, hydrophobia), to a change in the atmosphere, in the year 1783. It was said to have been imported, but experience, he says, proved the fact to be otherwise[39].
“This latent malignity in the atmosphere (says Baron Vansweiten) is known only by its effects, and cannot easily be reduced to any known species of acrimony.” In another place he says, “It seems certain that this unknown matter disposes all the humours to a sudden and bad putrefaction[40].”