On Malaria. 813 



already noticed that odour was not necessary to the existence 

 of malaria ; and the proof is, that while all such putrefying 

 matters, even to marshes, possess as much smell in winter as 

 in summer, the poison is produced only in hot weather. The 

 other is, as to mud, that, without any visible vegetation, not 

 only does its exposure to the sun in summer produce malaria 

 and fevers, but that this can be disengaged, even through the 

 water, provided that it is not very deep, and without absolute 

 exposure. Thus, in the former case, have some of the most 

 severe epidemics on record been produced by the stinking of 

 lakes and rivers, and the exposure of their mud ; as also hap- 

 pens often, and in the tropical climates very especially, from 

 that brief exposure which follows the recess of the tide : while, 

 in the West Indies, it is observed that fevers are invariably 

 produced by certain pools, as soon as they are so far diminished 

 in depth as to allow the air of the bottoms to escape through 

 the water. Now, though our climate is less active in this evil, 

 these are facts of value to us in the way of precaution, while 

 they are among the least suspected causes of evil ; since it 

 ,has been ascertained, that fevers are produced where no other 

 causes than these are present. And if I notice another fact, 

 that, in the West Indies, the mere exposure of the naked soil, 

 by removing stones which covered it, has produced a sudden 

 and deadly fever ; so have I, in this country, seen agues pro- 

 duced, immediately and decidedly, by the simple and little- 

 suspected accident of the inundation and drying of a cellar. 



But of fevers produced by the exposure of mud containing 

 vegetable matter, the most frequent instances in our own 

 country are those which occur in tide-harbours. In the 

 warmer climates, this is as notorious and deadly a cause as 

 any one that exists : and under this head, nothing can be more 

 notorious than that which occurs in the tide- rivers of Africa 

 and the East, or within the tropics generally ; since this is the 

 very analysis of those most pestilential of all spots, mangrove 

 sea-beaches and rivers. Here, there is no proper vegetation in 

 contact with the water, whether that be fresh or salt, as the 

 stems of the trees rise out of the naked mud : while it is 

 ascertained by endless experience, that such a river or beach 

 is safe as long as the mud is covered, but that the fever seizes 



APRIL— JUJfS, 1827. . Y 



