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is collected. These reservoirs of muddy and

stagnant water are considered by M. M. Comoto, Ximenez, Mocilio, and other intelligent physicians who have examined before me the causes of the insalubrity of Vera Cruz, as so many sources of infection. I shall not name here the marshes known by the name of the Cienega Boticaria, behind the powder magazine, the Laguna de la Hormiga, the Espartal, the Cienega de Arjóna, and the marsh of la Tembladera situated between the road of Rebenton and the Callejones de Aguas-largas. At the foot of the hillocks we find only small shrubs of croton and desmanthus, the euphorbia tithymaloides, the capraoia biflora, the jatropha with cotton-tree leaves, and ipomoca of which the stalk and flowers hardly rise above the arid sand which they cover. Wherever this sand is bathed by the water of the marshes which overflow in the rainy season, the vegetation becomes more vigorous. The rhizophora mangle, the coccoloba, pothos, arum, and other plants, which vegetate in a humid soil charged

with saline particles, form scattered thickets.

These low and marshy places are the more to

be feared as they are not constantly covered with water. A bed of dead leaves mixed with

fruits, roots, larvae of aquatic insects, and

other collections of animal matter, enter into

fermentation, in proportion as they become

heated by the rays of a burning sun. In another place I shall mention the experiments made by me while I staid at Cumana, on the action of the roots of the mangle on the ambient air, so long as they remain slightly moistened and exposed to the light; and these experiments will clear up in some degree the remarkable phenomenon anciently observed in both Indies, that of all the places where the manchineel and the mangle vegetate with vigour, the most unhealthy are those where the roots of those trees are not constantly covered with water. The putrefaction of vegetable matter is in general the more to be dreaded under the tropics, as the number of astringent plants is very considerable there, and as these plants contain in their bark and roots much animal matter combined with tan. * - * : *. If there are undoubted existing causes of the insalubrity of the air in the soil which surrounds Vera Cruz, , it cannot, however, be denied that there are others within the very town itself. The population of Vera Cruz is too great for the small extent of ground which the city occupies. Sixteen thousand inhabitants are confined within a space of 500,000

* Vauquelin, on the tan of gelatine and albumine. Annales du Museum, t. xv. p. 77.

square metres"; for Vera Cruz forms a semicircle of which the radius is not 600 metres. As the greatest part of the houses have only one story above the ground-floor, it follows that among the lower orders the number of persons inhabiting the same apartment is very considerable. The streets are broad, straight, the longest in a direction from the north-west to the south-east, and the shorter or cross streets from south-west to north-east; but as the town is surrounded with a high wall, there is little or no circulation of air. The breeze which blows feebly during summer from the south-east and east-south-east, is only felt on the terraces of the houses; and the inhabitants, whom the north wind frequently prevents in winter from crossing the streets, breathe nothing in the hot season but a stagnant and burning air. The strangers who frequent Vera Cruz have greatly exaggeratedt 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 * 5,361,988 square feet. Trans. + Thorne in the American Med. Repos. t. xxx. p. 46. Luzuriaga de la calentura biliosa, t. i. p. 65. (Translation

of the work of Benjamin Rush, enriched with the observations of M. Luzuriaga.)

the south of Europe; but as it is frequented by thousands of Europeans not seasoned to the climate, and situated under a burning sky, and surrounded by small marshes from whose emanations the air is infected, the fatal effects of the epidemics will not diminish till the police shall have continued to display its activity for a long succession of years. An intimate connection is observed on the coast of Mexico between the march of diseases, and the variations of the temperature of the atmosphere. Two seasons are only 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 farthest 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 months reaches 24° of the centigrade thermometer. t In December, January, and February, the heat remains below this limit; and accordingly it seldom happens that the yellow fever does not entirely disap

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pear 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 also on the production of the miasmata, which are formed in the environs of Vera Cruz. The entry and termination 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 accumulated in marshy situations. More than 1870 millimetres of rainwater " fall annually at Vera Cruz; and in the month of July, 1808, alone, an accurate observer, M. Costanzo, colonel of the corps of engineers, collected more than 880 millimetrest, . which is only one-third less than the quantity which falls at London during the whole year.

* 73° 6' inches. Trans. f 14° 9’ inches. Trans,

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