S4 Influence of Atmospheric Temperature 



pefature is only indirectly concerned.* And though this evi- 

 dence be notoriously imperfect, yet is it valuable in the direc- 

 tion thus given to further inquiry. We have no direct cogni- 

 zance of those miasmata, whether of animal or vegetable origin, 

 or simply chemical in kind, which form the material of epide- 

 mic disease; but we know that such material emanations 

 exist ; that they differ in different localities ; and that varia- 

 tion of temperature is the condition seemingly most essen- 

 tial to their several forms and various activity. We have evi- 

 dence, both experimental and of natural occurrence, of the 

 effects of a certain degree of heat in producing or evolving these 

 agents ; and of a higher degree in destroying them, or suspend- 

 ing their action. Such results might be inferred as probable, 

 from what we have cause to presume of their nature ; looking 

 here, as the nearest analogy, to the chemical constitution of the 

 known poisons, whether of animal or vegetable origin, — to the 

 feeble affinity by which their elements are generally united, — 

 and the facility with which they are decomposed, and enter 

 into new combinations from slight changes of temperature alone. 

 I need not refer to the many illustrations of this subject 

 furnished by the history of disease. They are continually mul- 

 tiplied, as observation becomes more exact ; and it is likely that 

 the estimate of effect from this source will enlarge in propor- 

 tion to our knowledge. The unequal influence of equal averages 

 of heat in different localities might itself suggest doubts whe- 

 ther too much is not attributed to its direct action, too little 

 to its operation through other agents. All examination of par- 

 ticular local conditions, such as soil, elevation, general humidity, 

 quantity and kind of vegetable growth, manner of culture, and 

 extent of running or stagnant water, shews the singular import- 



* Here I may again refer to Dr J. johnslon's book on the Diseases of 

 Tropical Climates, in which he shews how vaguely these relations of disease 

 and locality are often considered, and made the subject of inference. AVe 

 speak of hepatitis and remittent fevers as diseases of India, without advert- 

 ing to the fact that the true hepatitis (or tliat which is not a sequel to fever) 

 is ten times more prevalent on the coast of Coromandel, than in the plains 

 of Bengal ; — intermittent and remittent fevers in an equal ratio more fre- 

 quent in the latter locality. The medium annual temperature of Madras is 

 known to be amongst the highest on the globe (88° Fahr.) ; that of Calcutta 

 about ten degrees lower. 



