Meteorological and noSological table of Vera Cruz (lat. 19° 11 52') centigrade thermometer.

The mean temperature of Vera Cruz is 25.4, that of Mexico 17°, and that of Paris 11°. 3.

I should have added to this table, the progress of the thermometer at Philadelphia, and the number of individuals who died there of the yellow fever each month, if I could have procured observations sufficient to give the mean temperature of the different months of the year 1803. In temperate climates, results drawn from the greatest and smallest elevations of the thermometer at certain periods give us no information respecting the mean temperature. This very simple and very old observation appears to have escaped a great number of the Physicians who entered upon the discussion of the question, whether the last epidemical diseases of Spain were occasioned by heats which might be considered as extraordinary in the south of Europe. It has been affirmed in many works, that the year 1790 was two degrees hotter than the years 1799 and 1800, because in the two last years, the thermometer only rose at Cadiz to 28° and 30°. 5*, while in 1790 it rose to 32°.t The excellent meteorological observations of the Chevalier Chacon, published by M. Arejula, will throw the greatest light on this important matter, if we take the trouble of deducing the mean temperature of the months

# 820. 4 and 860. 2 of Fahr. Trans.
t 890. 6 of Fahr. Trans.

from it. Medicine can only be aided by natural philosophy, when we adopt accurate methods for examining the influences of heat, humidity, and the electrical tension of the air, on the progress of diseases. We have traced the progress which the yellow fever of Vera Cruz generally follows; and we have seen, that on an average the epidemic ceases to rage, when, at the commencement of the north winds, the mean temperature of the months falls below 24°, * The phenomena of life are no doubt subject to immutable laws; but we know so little of the whole of the conditions under which disease is introduced into the functions of the organs, that the pathological phenomena appear to exhibit to us in their succession the strangest irregularities. When the vomito commences to rage at Vera Cruz during summer with great violence, we see it prevail during the whole winter; the lowness of the temperature then diminishes the disease, but does not entirely extinguish it. f The year 1803, in which the mortality was very small, affords a striking example of this sort. * 750 of Fahr. Trans. f The feeling of heat, and the influence of temperature on the organs, depending on the degree of habitual excitation, the same air which passes at Vera Cruz for cold,

We see from the table which I have already given, that every month there were some individuals attacked by the vomito; but that during the winter of 1803, Vera Cruz was still suffering from the epidemic, which during the preceding summer had burst forth with such extraordinary force. The vomito not having been very frequent during the summer of 1803, ceased altogether in the beginning of the year 1804. When M. Bonpland and myself descended in the last days of the month of February, from Xalapa to Vera Cruz, the town contained no person under the yellow fever, and a few days afterwards, in a season when the north wind still blew with impetuosity, and when the thermometer never rose to 190 *, we were conducted by M. Commoto to the hospital of Saint Sebastian, to the bed side of a dying man, a very swarthy Mexico mestizo, who was a muleteer, and came from the table land of Perote, and who had been attacked by the vomito in crossing the plain which separates la Antigua from Vera Cruz. ~ + Fortunately these cases in which the disease is sporadical is in winter exceedingly rare ; and a true epidemic never developes itself at Vera Cruz, but when the heats of summer begin to be felt, and when the thermometer frequently rises above 24°. The same progress of the yellow fever is observable in the United States. Mr. Carey has no doubt observed *, that the weeks in which the thermometer was highest at Philadelphia, were not always those in which the mortality was the greatest; but this observation merely proves, that the effects of the temperature and the humidity of the atmosphere on the production of miasmata, and on the state of irritability of the organs, are not always instantaneous. I am far from considering an extreme heat as the only and true cause of the vomito; but how can it be denied, that there exists in places where the disease is endemical, an intimate connection between the state of the atmosphere and the progress of the disease ? It is incontestible 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 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 imme