328 Mr. Addison's Remarks on the Influence of Terrestrial 



In this country the pernicious nature of the morning and 

 evening mists formed over low grounds has been observed, 

 and in hotter climates I need scarcely say that their influence 

 in generating fever is as notorious as any of the best established 

 facts on this subject; and the progress of the sun upwards 

 being a remedy for the morning mists, and the day altogether 

 for those of the night, seems to confirm the opinion, that a 

 watery and moist atmosphere is the active conductor or repo- 

 sitory of malaria ; and that when the former is dissipated, the 

 latter is checked in its progress ; when the one is entirely di- 

 spersed, the other may be destroyed : so that the matter of 

 malaria seems to be defined as to its place and extent by va- 

 pour and mist*. 



That the diseases arising from miasmata in the air do some- 

 times cease in a definite and sudden line, and terminate also 

 at particular altitudes, has often been observed and recorded ; 

 and these remarkable instances cannot be satisfactorily ex- 

 plained upon any other supposition than that afforded by the 

 radiation of caloric. To explain their cessation in the former 

 instance, we may remark, that that depression of temperature 

 which ensues at night over a good radiating surface, may be 

 sufficient to render active the miasms existing in the air ; while 

 over others, less powerful in the dissipation of caloric, the de- 

 pression of temperature may not be sufficient; and it is probable 

 that in many cases an atmosphere rendered prejudicial by the 

 one, is again made innoxious by passing over the other. With 

 respect to altitude, I have before shown that slight elevations 

 are frequently a protection against the heavy miasmatous air 

 which subsides to the lowest situations. 



But to place this important subject in the clearest possible 

 light, let me endeavour (by an appeal to some well-known 

 chemical facts) to set forth the nature of the connection ex- 

 isting between free caloric and the matter of malaria. Let us 

 suppose that the former exerts over the latter an influence ana- 

 logous to that exercised by an acid over an alkali (neutralizing 

 its qualities and destroying its effects), and we shall immedi- 

 ately perceive that the mere presence of malarious matters in 

 the air may not be sufficient to excite in the human body 

 a state of disorder or disease: carry the reasoning a little 

 further, and then we can fully understand the way in which 

 radiation proves injurious. Are we not warranted in conclu- 

 ding, from those facts which observation and experience have 

 discovered to us, that similar phaenomena are exhibited in the 

 relations subsisting between the matter of heat and miasmatous 



* Vide Macculloch's Essay, pp. 259 and 274. 



effluvia 



