152 TRINIDAD. 



separately from air and heat ; but we are warranted in concluding, 

 analogically, from its effects on the healthy growth of plants, and 

 the metamorphoses of batracians, that it must materially influence 

 certain functions. I do not, therefore, hesitate to affirm, that the 

 evil effects of confinement, in dark rooms or dwellings, must be 

 partly attributed to the absence or want of light ; whilst to the 

 presence of that agent may be partly traced the beneficial results 

 of exercise in the open air, particularly in the case of those who 

 have the misfortune of being born with a lymphatic temperament. 



Besides the general influence exercised on the human frame 

 by a high temperature, combined with humidity, there may exist 

 in the air certain substances which, in the form of miasmatic ema- 

 nations, exercise a most material agency in the development of 

 maladies, and towards the salubrity of a country. 



A warm, damp atmosphere is the condition naturally most 

 favourable to the decomposition of organic substances, either 

 animal or vegetable ; and as the gaseous exhalations evolved from 

 such decompositions are more readily held in suspension in such 

 an atmosphere, it may be considered, where suitable affinities 

 exist, as highly predisposing to very serious diseases, and especially 

 to the almost innumerable series of periodical affections. 



Emanations arising from the decomposition of vegetable 

 matters are particularly noxious ; and yet, when they are allowed 

 to decay in a dry air, they do not disengage any deleterious prin- 

 ciples. In order to generate those principles, they must undergo 

 the process of decay in stagnant water, thus forming swamps. 

 Swamp- water is, generally, fetid ; but fetidity is no positive mark 

 of the deleterious qualities of a swamp. 



Swamps or marshes are created by collections of standing 

 water, either fresh or salt ; it may be said, however, that purely 

 salt-water marshes do not exist, since they are almost invariably 

 formed by an admixture of fresh with salt water. The latter are 

 much more dangerous than merely fresh or salt water swamps, 

 whereas this admixture has for result to aid in the decomposition 

 of the organic matters contained in both. 



The following are the conditions necessary for the formation of 

 swamp effluvia : a damp, warm air, the ground neither too dry 

 nor too deeply covered with water. Hence the atmosphere of 

 these watery tracts always contains more or less of moisture, but 

 more during the night than the day; it also holds in suspension, 



