That the geographical position of the Cape de Verd Islands places them within the legitimate domain of Yellow Fever, and that this disease is no stranger to these islands, is admitted on all hands. According to Dr M‘William,
“The north-western part of the island, where Porto Sal Rey is situated, is low and flat, and almost wholly occupied by sand, which, blown up from the north-western shore through the water-courses, and other hollows, accumulates in mounds twenty and thirty feet high, which are drawn about and shifted by any little variation of the direction of the wind.”
On the flat between Porto Sal Rey and the village of Rabil, which is about four miles to the southward of Porto Sal Rey, Dr M‘William states that there is a point where the sea, when the waves are high—
“Breaks over the elevated beach, and penetrates through the shingle, so as to accumulate, and run inland in the form of a narrow creek, from 200 to 300 yards from the sea-shore. During the rainy season, this, in common with the other flats on the island, is inundated to a considerable extent, as is evident from the appearance of the soil in those places not covered with sand, as well as by the presence of a rude raised causeway, which the people have constructed over part of the hollow flat, to render it passable during the rains. * * * Near the town is a hollow flat, spread over an area of about a mile, with the same soil and subsoil as that in the town. The central part of this area is occupied by a salt pan, which contains not less than 300 troughs, each a foot deep, and about thirty feet square, into which the salt water is poured, there to evaporate and form salt. During and for some weeks after the rainy season, the whole of this space is more or less inundated. * * * The water is left to stagnate on the Rabil side, and as it dries up during the hot weather, little alluvial islets are from time to time exposed, which the people avail themselves of to raise a small crop of corn. Indeed the greater part of the ravine, from Rabil downwards, is in a state of rude cultivation, and contains large green fœtid pools, with all kinds of decomposing matter, the effluvia from which was most offensive when I was there in May, 1846.”
Experience has shown, that such a condition of sandy soil is as fruitful a source of endemic and malignant fever as a marsh or swamp. Dr Lind, who wrote nearly a century ago, expressly notices the unhealthiness of Boa Vista, particularly during the rainy season, stating that, “strangers who arrive here at this season are liable to be visited by a general sickness,” and instances its white sand as a mark of an unhealthy locality. Dr Fergusson confirms the correctness of this indication of insalubrity.
“That sandy soils,” he says, “should, in malarious climates, prove as productive of aggravated remittent fever as the swamp, has never been sufficiently explained. Certain it is, however, that they do so, in a marked and prominent degree. The Alemtejo and Algarve of Portugal—regions, I may say, altogether of sand—are the most prolific of fever of any in the Peninsula.”
Another instance is found in the unhealthiness of Vera Cruz, which is spoken of by McCulloch in the following words:—
“It is said to be the original seat of the Yellow Fever.” [Bulama?] “The city is well built and the streets clean, but it is surrounded by sand-hills and ponds of stagnant water, which, within the tropics, are quite enough to generate disease. The inhabitants and those accustomed to the climate are not subject to this formidable disease; but all strangers, even those from the Havannah and the West India Islands are liable to the infection. No precautions can prevent its attack, and many have died at Xalapa, on the road to Mexico, who merely passed through this pestilential spot.”
Dr King states, that if ever endemic fever derives its origin from a vitiated and malarious state of the atmosphere, Boa Vista abounds with the elements for its production. Among these he enumerates swamps and pools of stagnant water, in the immediate vicinity of Porto Sal Rey, and over the whole district of Rabil; patches of rich alluvial soil near the other villages, the recognized sources of noxious exhalations; the wretched food of the lower classes, and still more, the polluted atmosphere which they breathe in their crowded and ill-ventilated abodes, and the general disregard of cleanliness in their houses and streets, “a combination of morbid causes,” he says, “which would produce malignant fevers in any part of the world.”
The relative position of Boa Vista to the African coast would further naturally lead to the expectation that it must be subject to diseases of the same character, and no one disputes that this is the case. The residents of the island, military, medical, and civil, concur in stating that endemic, bilious remittent fever, prevails there more or less every year; that there is no season in which it does not carry off several of the inhabitants, and that it often prevails epidemically.