YFLLOW FEVER. 121 



by navigators, the American typhus (black vomit- 

 ing, or yellow fever) makes its appearance. These 

 persons, we may add, are not affected by it during 

 the passage ; it manifests itself only on the spot. 

 Has the constitution of the atmosphere been changed ? 

 asks Humboldt ; or, has a new form of disease de- 

 veloped itself in individuals whose excitability is 

 raised to a high pitch 1 



The malady forthwith attacks other Europeans 

 born in warmer countries. Immediate contact does 

 not increase the danger, nor does seclusion diminish 

 it. When the sick are removed to the interior, and 

 especially to cooler and more elevated places, they 

 do not communicate the typhus to the inhabitants. 

 Whenever a considerable diminution of temperature 

 occurs, the distemper usually ceases ; but it again 

 begins at the commencement of the hot season, 

 although no ship may have entered the harbour for 

 several months. 



The yellow fever disappears periodically at Ha- 

 vana and at Vera Cruz, when the north winds 

 carry the cold air of Canada towards the Mexican 

 Gulf ; but as Porto Cabello, La Guayra, New-Bar- 

 celona, and Cumana possess an extreme equality of 

 temperature, it is probable that it will become per- 

 manent there. Happily, the mortality has diminished 

 since the treatment has been varied according to the 

 modifications which the disease assumes. In well- 

 managed hospitals, the number of deaths is often 

 reduced to eighteen or fifteen in a hundred ; but when 

 the sick are crowded together the loss increases to 

 one -half, or even more. 



To the west of La Guayra there are several in- 

 dentations of the land which furnish excellent an- 

 chorage. The coast is granitic, and a great portion 

 of it extremely unhealthy. At Cape Blanco the 

 gneiss passes into mica-slate, containing beds of 

 chlorite-slate, in which garnets and magnetic sand 

 occur. On the road to Catia-the chlorite-slate is 

 L 



