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

Carey, Description of the malignant fever of Philadelphia, 1794. p. 38.

diate 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.

According to the information which I obtained during a long stay in America, and from the observations of M. M. Mackitrick, Walker, Rush, Valentin, Miller, and almost all the physicians who have practised both in the West India Islands, and the United States, I am inclined to believe that this disease is not contagious in its nature, either under the temperate zone*; or in the equinoctial regions of the New Continent. I say from its nature; for it is not contrary to the analogy which other pathological phenomena exhibit, that a malady not essentially contagious, may, under a certain influence of climate and seasons, by the accumulation of patients, and from their individual disposition, assume a new character. It appears that the exceptions, which are infinitely rare under the torrid zonet, are

* See two excellent memoirs of Mr. Stubbins Ffirth, of New Jersey, and Mr Edward Miller, of New York, on the non-contagious character of the yellow fever of the United States.

† Fiedler, über das gelbe Fieber nach eigenen Beobachtungen, p. 137-Pugnet, p. 393.

more particularly to be found under the temperate zone. In Spain, where in 1800 more than 47,000, and in 1804 more than 64,000 individuals fell victims to the yellow fever, "this disease was contagious, but only "in those places where it committed its ravages; for it has been proved by numerous "facts, and particularly from observations "made at Malaga, Alicant*, and Carthagena, "that affected persons did not communicate "the disease in the villages to which they "retired, although the climate was the same "there as that of the contagious towns." This opinion is the result of the observations of the enlightened commissiont sent by the French government into Spain, in 1806, for the purpose of investigating the developement of the epidemic.

When we successively turn our eyes to

* Bally, Opinion sur la Contagion de la fievre jaune, 1810,

p. 40.

† M. M. Dumeril, Bally, and Nysten. It is not either in any way ascertained that the yellow fever was introduced into Spain by the Jupiter polacra from Vera Cruz, or the Dauphin Corvette built at Baltimore, in which Don Pablo Valiente, the intendant of the Havannah, and Don Josef Caro, the physician, were embarked. (Arejula. p. 251.) Three distinguished physicians of Cadiz, M. M. Ammeller, Delon, and Gonzales, believe that the yellow fever developed itself spontaneously in Spain: a disease may be contagious, without being imported.

the equinoctial regions of America, to the United States, and to those parts of Europe where the yellow fever has exercised its ravages, we see, that notwithstanding the equality of temperature which prevails during several months of the year, under zones very remote from one another, the malady assumes a different appearance. Between the tropics its uncontagious character is almost universally acknowledged. In the United States this character has been warmly contested by the faculty of medicine of the University of Philadelphia, as well as by M. M. Wistar, Blane, Cathral, and other distinguished physicians. At last, advancing north-eastwards to Spain, we find the yellow fever undoubtedly contagious, as is proved by the examples of persons who preserved themselves by shutting themselves up, although they were in the very heart of the disease.

The farm of l'Encero near Vera Cruz, which I found to be 928* metres, elevated above the level of the ocean, is the superior limit of the vomito. We have already observed that the Mexican oaks descend no farther than that place, being unable to vegetate in a heat sufficient to develope the germ of the yellow fever. Indivi

* 3043 feet. Trans.

1

duals born and brought up at Vera Cruz, are not subject to this disease; and it is the same with the inhabitants of the Havanah, who do not quit their country; but it happens that merchants, born in the island of Cuba, and who have inhabited it for a great number of years, are attacked with the vomito prieto, when their affairs oblige them to visit the port of Vera Cruz during the months of August and September, when the epidemic is at its height. In the same manner Spanish Mexicans, natives of Vera Cruz, have been seen to fall victims to the vomito at Havanah, Jamaica, or the United States. These facts are no doubt very remarkable, when we consider them with respect to the modifications which the irritability of the organs exhibits. Notwithstanding the great analogy which the climate of Vera Cruz bears to that of the island of Cuba, the inhabitant of the Mexican coast, insensible to the miasmata of the air of his native country, falls under the exciting and pathogenical causes which act on him at Jamaica and the Havanah. It is probable that under the same parallel, the gaseous emanations which produce the same diseases, are almost the same; but that a slight difference is sufficient to throw disorder into the vital functions, and to determine that particular succession of phenomena, by