On Malaria. 309 



lence of its effects as we advance towards warmer and tropical cli- 

 mates. The degree of heat in Calcutta, during the prevalence of 

 malignant intermittents was from 86° to 76°, Fahr. In Syria it was 

 86°, and increasing.* At Bassora in 1780, previous to a most fright- 

 ful and malignant intermittent, the thermometer rose from 115° to 

 156° in the shade. f On Long Island 1828, in August, just before 

 the remitting fever became epidemic, it was from 91° to 73°. J 



But in temperate climates it is not during the actual presence of 

 the heat that the pestilential power is most injurious. The Italian 

 peasant takes a siesta upon the ground at noon and escapes unhurt.§ 

 The poisonous gases and vapors at that hour, are so rarefied, or diffu- 

 sed, or in common phrase, so dried up, that they are harmless ; but 

 when the air is cooled sufficiently to condense the aqueous vapors, and 

 they descend in dews, imparting a delightful freshness, then it is that 

 the insidious and baneful poison is abroad. Those peasants " to whom 

 tlie earth serves as a bed, after the cold dews have descended upon it, 

 and who pass the night on the moist turf," seldom, if ever, escape ; 

 and laborers who incautiously sit upon the ground, are sometimes 

 struck with apoplexy, or even with death. On this principle it is 

 easy to see, why the diseases proceeding from this cause, are more 

 aggravated in autumn. During the summer, it is not generally danger- 

 ous, except in the evening and morning ; but the heat of summer having 



* Bancroft on fevers. t Ty tier on plague. 



:j; I am indebted to Mr. Kellogg, Principal of the Academy at Erasmus Hall, Flat- 

 bush, Long Island, for the following accurate table, which shows the effect of heat 

 and drought in eliciting and concentrating malaria in our own climate. It includes 

 the amount of rain which fell in June, July, and August, and the summer temper-* 

 ature of four consecutive years. 



Rain during the months of 



§ Chateauvieux's Agricultural Travels. 



