9. The continuance of hard labour. The miasmata which produce malignant fevers sometimes possess so much force, that the least addition to it, even from customary acts of labour, is sufficient to excite the disease. In this case, safety should be sought in retirement, more especially by those persons whose occupations expose them to the heat of fires, and the rays of the sun, such as hatters, smiths, bricklayers, and house and ship carpenters. The wealthy inhabitants of Constantinople and Smyrna erroneously suppose they escape the contagion of the plague, by shutting themselves up in their houses during its prevalence. They owe their preservation chiefly to their being removed, by an exemption from care and business, from all its exciting causes. Most of the nobility and gentry of Moscow, by these means escaped a plague which carried off 27,000 persons in that city, in the year 1771, and many whole families in Philadelphia were indebted for their safety to the same precautions in the year 1793. Confinement is more certain in its beneficial effects, when persons occupy the upper stories only of their houses. The inhabitants of St. Lucia, Dr. Chisholm says, by this means often escape the yellow fever of that island. Such is the difference between the healthiness of the upper and lower stories of a house, that, travellers tell us, birds live in the former, and die in the latter, during the prevalence of a plague in the eastern countries.
All the exciting causes that have been enumerated should be avoided with double care three days before, and three days after, as well as on the days of the full and change of the moon. The reason for this caution was given in the account of the yellow fever in Philadelphia in the year 1797.
To persons who have retired from infected cities, or countries, it will be necessary to suggest a caution, not to visit them while the malignant fever from which they fled prevails in them. Dr. Dow informed me, in his visit to Philadelphia in the year 1800, that the natives and old citizens of New-Orleans who retired into the country, and returned during the prevalence of the yellow fever in that city, the year before, were often affected by it, while all such persons as did not change their residence, escaped it. The danger from visiting an infected city is greater to persons who breathe an atmosphere of a uniform temperature, than one that is subject to alternate changes in its degrees of heat and cold. The inhabitants of Mexico, Baron Humboldt informed me, who descend from their elevated situation, where the thermometer seldom varies more than ten degrees in the year, and visit Vera Cruz during the prevalence of the yellow fever in that city, are much oftener affected by it than the new comers from the variable climates of European countries. But the habits of insensibility to the impressions of the miasmata of this disease in one country, do not always protect the system from their action in another. The same illustrious traveller informed me, that the inhabitants of the Havannah who visit Vera Cruz, and the inhabitants of Vera Cruz who visit the Havannah, are affected in common with strangers with the fever of those places.
I shall take leave of this part of our subject, by adding, that I am so much impressed with a belief in the general, and almost necessary connection of an exciting cause with a yellow fever, that were I to enter a city, and meet its inhabitants under the first impressions of terror and distress from its appearance, my advice to them should be, “Beware, not of contagion, for the yellow fever of our country is not contagious, nor of putrid exhalations, when the duties of humanity or consanguinity require your attendance, but BEWARE OF EXCITING CAUSES!”
In the mild grades of the summer and autumnal fevers of the United States, the means of prevention should be different from those which have been recommended to prevent the yellow fever. They consist of such things as gently invigorate the system, and thus create an action superior to that which the miasmata have excited in it. The means commonly employed for this purpose are,
1. Cordial diet and drinks; consisting of salted meat, and fish, with a moderate quantity of wine and malt liquors. Dr. Blane says, the British soldiers who lived upon salt meat, during the American war, were much less afflicted with the intermitting fever than the neighbouring country people; and, it is well known, the American army was much less afflicted with summer and autumnal fevers, after they exchanged their fresh meat for rations of salted beef and pork. Ardent spirits should be used cautiously, for, when taken long enough to do good, they create a dangerous attachment to them. A strong infusion of any bitter herb in water, taken upon an empty stomach, is a cheap substitute for all the above liquors where they cannot be afforded. The Peruvian bark has in many instances been used with success as a preventive of the mild grades of the summer and autumnal fevers of our country.
2. An equable and constant perspiration. This should be kept up by all the means formerly mentioned for that purpose.
3. Avoiding certain exciting causes, particularly great heat and cold, fatigue, long intervals between meals, intemperance, and the morning and evening air, more especially during the lunar periods formerly mentioned. Dr. Lind says, the farmers of Holdernesse, in England, who go out early to their work, are seldom long lived, probably from their constitutions being destroyed by frequent attacks of intermitting fevers, to which that practice exposes them. Where peculiar circumstances of business render it necessary for persons to inhale the morning air, care should be taken never to do it without first eating a cordial breakfast.