Mr. T. Hopkins's Observations on Malaria. 119 



striking, but explicable on the supposition that obstruction of 

 the ordinary amount of evaporation is the evil experienced. 

 By the natives, the moisture which cannot find its way out of 

 the body by evaporation, maybe thrown off by exudation, 

 while the temperature of the body may be kept down by suit- 

 able regimen. But a stranger coming from a cold and dry 

 climate, accustomed to take considerable quantities of heating 

 food into his stomach, and to have much caloric carried off 

 by evaporation, has a sudden stop put to this most important 

 process ; the water and fire I'emain in the system, and fever is 

 the result. Nature deranged in her operations struggles with 

 these new circumstances. The stomach refuses food, because 

 to take it would be heaping new fuel on the body already 

 overcharged with fire. A copious perspiration by exudation 

 sometimes takes place, but mostly when the superabundant 

 fire has been dissipated. Inquiry may possibly show that this 

 is the ordinary expedient of nature under the influence of a 

 heated atmosphere charged with an excess of steam. Per- 

 haps as evaporation is checked exudation increases, and with 

 suitable regimen, the system may in time become adapted to 

 the climate. It is observed that the natives of such climates 

 appear to have a clammy moisture on their skins, and their 

 complexions are sallow. The black race are the least affected 

 by a hot and damp atmosphere ; does exudation with them 

 supply the place of evaporation in a greater degree than 

 among the European races ? 



If the foregoing observations be well founded, it may be 

 presumed that in those parts of the world which have a high 

 temperature malaria will be found, and especially when the 

 air has been some time stagnant, in the following situations, 

 viz. 



1. Over the open sea. It will be mild here because the 



temperature is not very high. 



2. Over slowly moving rivers. They will be somewhat 



more heated by the aun than the sea is, and will 

 therefore evaporate more freely. 



3. Over meadows and woods. The great extent of moist 



surfaces admits of great evaporation from these, 

 -t. Over shallow stagnant water. The temperature of the wa- 

 ter will be high, and evaporation consequently great. 



5. Over tide sands and muds. These become very hot, and 



consequently evaporate copiously. 



6. Over marshes. These combine great heat, extensive 



surface for evaporation, and abundant moisture. 

 With due attention to local influences 1 would then propose, 

 in order to ascertain whether malaria be or be not the effect 



