YELLOW FEVER.

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found to be 3043 feet above the level of the ocean, is the highest limit of the vomito. We have already observed that the Mexican oaks descend no further than that place, being unable to vegetate in a heat sufficient to develop the germ of the yellow fever. Individuals born and brought up at Vera Cruz are not subject to this disease.

The Whites and the Mestizos who inhabit the interior table-land of Mexico, of which the mean temperature is 60° and 62° Fahr., and where the thermometer sometimes falls below the freezing point, are more liable to contract the vomito, when they descend from l'Encero to the Plan del Rio, and from thence to la Antigua and the port of Vera Cruz, than the Europeans or inhabitants of the United States, who come by sea. The latter, passing by degrees into the southern latitudes, are gradually prepared for the great heats which they experience on landing; but the Spanish Mexicans, on the other hand, suddenly change their climate, when, in the space of a few hours, they are transported from the temperate region to the torrid zone. The environs of Vera Cruz are frightfully arid. On arriving by the Xalapa road, we find near la Antigua, a few cocoa trees which ornament the gardens of that village; and they are the last great trees to be discovered in the desert. The excessive heat which prevails in the town is increased by the hillocks of moving sands (meganos) formed by the impetuosity of the north winds, and sur

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106 CHARACTER OF THE FEVER OF VERA CRUZ.

rounding it on the south and south-west side. The suffocating heat which prevails in this parched and naked plain, has a powerful effect on individuals whose nervous system has never been accustomed to so violent an irritation. The heat, added to the fatigues of the journey, disposes the organs more easily to receive the deleterious miasmata of the yellow fever: the ravages of that pestilential malady will be greatly diminished, therefore, by shortening that part of the road which crosses the arid plains of the sea coast.

Persons born at Vera Cruz are not liable to contract the vomito in their native country; and in this respect they possess a great advantage over the inhabitants of the United States, who suffer from the insalubrity of their own climate. Another advantage of the torrid zone is, that the Europeans, and in general all individuals born in temperate climates, are never twice attacked with the yellow fever.

It is however certain that the vomito, which is endemical at Vera Cruz, Carthagena, and the Havannah, is the same disease with the yellow fever, which since the year 1793 has never ceased to afflict the inhabitants of the United States.

It is incontestable that the vomito is not contagious at Vera Cruz. In most countries, the common people consider many diseases as contagious which are of a very different character; but no popular opinion in Mexico has ever interdicted the

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stranger not seasoned to the climate from approaching the beds of those attacked by the vomito. No fact can be cited to render it probable that the immediate contact or breath of the dying person is dangerous to those not seasoned to the climate, who may attend on the patient. On the continent of equinoctial America, the yellow fever is not more contagious than the intermittent fevers of Europe.

Pringle, Lind, and other distinguished physicians, consider our summer and autumnal bilious affections as the first degree of yellow fever. A feeble analogy is also discoverable in the pernicious intermittent fevers which prevail in Italy. In the low regions of Mexico, as well as in Europe, the sudden suppression of perspiration is one of the principal occasional causes of the gastric or bilious fe

vers.

The strangers who frequent Vera Cruz have greatly exaggerated the dirtiness of the inhabitants. For some time the police has taken measures for the preservation of the salubrity of the air; and Vera Cruz is at present not so dirty as many of the towns of the south of Europe; but these precautions must be continued for some years before their good effects will be sensibly felt.

An intimate connexion is observed on the coast of Mexico between the progress of diseases, and the variations of the temperature of the atmosphere. Two seasons only are known at Vera Cruz, that of the tempest of the north (los Nortes) from the

autumnal to the spring equinox, and that of the breezes or south winds (brizas), which blow with considerable regularity between March and September. The month of January is the coldest in the year, because it is furthest from the two periods in which the sun passes through the zenith of Vera Cruz. The vomito generally begins first to rage in that town when the mean temperature of the month reaches 75° Fahr. In December, January, and February, the heat remains below this limit; and accordingly it seldom happens that the yellow fever does not entirely disappear in that season when a very sensible cold is frequently felt. The strong heats begin in the month of March, and the epidemical scourge begins at the same time. Although May is warmer than September and October, it is however in the two last months that the vomito commits the greatest ravages; for in every epidemic it requires a certain time before the germ of the disease is developed in all its energy; and the rains, which last from the month of June to the month of September, have an undoubted influence on the production of the miasmata which are formed in the environs of Vera Cruz.

The beginning and the close of the rainy season are dreaded the most under the tropics, because an excessive humidity arrests, almost as much as a great drought, the progress of putrefaction of the vegetable and animal substances which are accumu

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lated in marshy situations. More than 90 inches of rain-water fall annually at Vera Cruz; and in the month of July 1803 alone, an accurate observer, M. Costanzo, colonel of the corps of engineers, collected more than 25 inches, which is only one-third less than the quantity which falls at London during the whole year.

It is a very remarkable fact, that during the eight years which preceded 1794, there was not a single example of vomito, although the concourse of Europeans and Mexicans from the interior was extremely great.