In some constitutions, the miasmata were at once a remote, a predisposing, and an exciting cause of the disease; hence some persons were affected by them, who had not departed in any instance from their ordinary habits of living, as to diet, dress, and exercise. But it was more frequently brought on by those causes acting in succession to each other.
I shall here refer the reader to the principles laid down in the outlines of the theory of fever, for an account of the manner in which the system was predisposed to this disease, by the debility induced by the reduction of its excitement, by action and abstraction, and by subsequent depression. Where a predisposition was thus produced, the fever was excited by the following causes, acting directly or indirectly upon the system. Where this predisposition did not exist, the exciting causes produced both the predisposition and the disease. They were,
1. Great labour, or exercises of body or mind, in walking, riding, watching, or the like. It was labour which excited the disease so universally among the lower class of people. A long walk often induced it. Few escaped it after a day, or even a few hours spent in gunning. A hard trotting horse brought it on two of my patients. Perhaps riding on horseback, and in the sun, was the exciting cause of the disease in most of the citizens and strangers who were affected by it in their flight from the city. A fall excited it in a girl, and a stroke upon the head excited it in a young man who came under my care. Many people were seized with the disease in consequence of their exertions on the night of the 7th of September, in extinguishing the fire which consumed Mr. Dobson's printing-office, and even the less violent exercise of working the fire engines, for the purpose of laying the dust in the streets, added frequently to the number of the sick.
2. Heat, from every cause, but more especially the heat of the sun, was a very common exciting cause of the disease. The register of the weather during the latter end of August, the whole of September, and the first two weeks in October will show how much the heat of the sun must have contributed to excite the disease, more especially among labouring people. The heat of common fires likewise became a frequent cause of the activity of the miasmata where they had been received into the body; hence the greater mortality of the disease among bakers, blacksmiths, and hatters than among any other class of people.
3. Intemperance in eating or drinking. A plentiful meal, and a few extra glasses of wine seldom failed of exciting the fever. But where the body was strongly impregnated with the seeds of the disease, even the smallest deviation from the customary stimulus of diet, in respect to quality or quantity, roused them into action. A supper of twelve oysters in one, and of but three in another, of my patients produced the disease. Half an ounce of meat excited it in a lady who had lived, by my advice, for two weeks upon milk and vegetables, and even a supper of sallad, dressed after the French fashion, excited it in one of Dr. Mease's patients.
4. Fear. In many people the disease was excited by a sudden paroxysm of fear; but I saw some remarkable instances where timid people escaped the disease, although they were constantly exposed to it. Perhaps a moderate degree of fear served to counteract the excessive stimulus of the miasmata, and thereby to preserve the body in a state of healthy equilibrium. I am certain that fear did no harm after the disease was formed, in those cases where great morbid excess of action had taken place. It was an early discovery of this fact which led me not to conceal from my patients the true name of this fever, when I was called to them on the day of their being attacked by it. The fear co-operated with some of my remedies (to be mentioned hereafter) in reducing the morbid excitement of the arterial system.
5. Grief. It was remarkable that the disease was not excited in many cases in the attendants upon the sick, while there was a hope of their recovery. The grief which followed the extinction of hope, by death, frequently produced it within a day or two afterwards, and that not in one person only, but often in most of the near relations of the deceased. But the disease was also produced by a change in the state of the mind directly opposite to that which has been mentioned. Many persons that attended patients who recovered, were seized with the disease a day or two after they were relieved from the toils and anxiety of nursing. The collapse of the mind from the abstraction of the stimulus of hope and desire, by their ample gratification, probably produced that debility, and loss of the equilibrium in the system, which favoured the activity of the miasmata in the manner formerly mentioned[14].
The effects of both the states of mind which have been described, have been happily illustrated by two facts which are recorded by Dr. Jackson[15]. He tells us, that the garrisons of Savannah and York-Town were both healthy during the siege of those towns, but that the former became sickly as soon as the French and American armies retreated, from before it, and the latter, immediately after its capitulation.
6. Cold. Its action, in exciting the disease, depended upon the diminution of the necessary and natural heat of the body, and thereby so far destroying the equilibrium of the system, as to enable the miasmata to produce excessive or convulsive motions in the blood-vessels. The night air, even in the warm month of September, was often so cool as to excite the disease, where the dress and bed-clothes were not accommodated to it. It was excited in one case by a person's only wetting his feet, in the month of October, and neglecting afterwards to change his shoes and stockings. Every change in the weather, that was short of producing frost, evidently increased the number of sick people. This was obvious after the 18th and 19th of September, when the mercury fell to 44° and 45°. The hopes of the city received a severe disappointment upon this occasion, for I well recollect there was a general expectation that this change in the weather would have checked the disease. The same increase of the number of sick was observed to follow the cool weather which succeeded the 6th and 7th of October, on which days the mercury fell to 43° and 46°.