From Humboldt’s Essay on New Spain.

“In the low countries of Mexico, as in Europe, the sudden suppression of transpiration is one of the principal occasional causes of gastric or bilious fevers, and especially of Cholera Morbus, which exhibits symptoms so frightful.

The climate of Acapulco, whose temperament is uniform throughout the different seasons of the year, permits these sudden suppressions of transpiration, from the singular coolness which prevails there for several hours before sun rising.

On those coasts strangers not acclimated, if, being slightly clothed, they travel in the night, or sleep in open air.

In Cumana, and other places of equinoctial climate, the temperature does not diminish towards sun-rising more than one or two degrees of the Centigrade thermometer (1-8 to 3-6, of Fahrenheit.)

In the day time the thermometer is, there, at 82 to 84 of F. and in the night at 73 to 75.

At Acapulco I have found the temperature in the day-time at 84 to 86—during the night it is about 79—but, for about three hours before sun-rising, it sinks rapidly to 60 or 64.

“This change produces a very sensible impression on the organs.

In no other part of the tropical regions have I felt so great coolness in the latter part of the night; we seem to pass suddenly from summer to autumn, and yet the sun has hardly risen before we complain of the heat.

In a climate in which health depends chiefly on the functions of the skin, and in which the organs are affected with the slightest changes of temperature, a diminution of 18 or 20 degrees produces suppressions of transpiration, extremely dangerous to Europeans not acclimated.”

Is it not very proper to attribute many, if not most, of our diseases in the United-States, to the same cause, viz: the sensible diminution of temperature in the latter part of the night, during August and September?