274 ON THE NATURE AND HISTORY 



the most frequent and destructive source of fever to the hu- 

 man race, as that form of fever to which it gives rise, rages 

 throughout the world wherever a marshy surface has been ex- 

 posed for a sufficient length of time to the action of a powerful 

 sun. I have said for a sufficient length of time ; because, as 

 will presently be seen, the marsh must cease to be a marsh, in 

 the common acceptation of the word, and the sensible putre- 

 faction of water and vegetables must alike be impossible, be- 

 fore its surface can become deleterious. It will also be seen, 

 that a healthy condition of soil, in these pestiferous regions, is 

 infallibly regained by the restoration of the marshy surface in 

 its utmost vigour of vegetable growth and decay. The pre- 

 vious marshy surface, or rather the previous abundance of wa- 

 ter, is, however, an indispensable requisite preliminary, in all 

 situations, to the production and evolvement of the marsh poi- 

 son. A short review of the circumstances, which, under my 

 own observation, attended our armies on service during the 

 last war, will, I hope, render these seemingly paradoxical opi- 

 nions intelligible to the Society. 



The first time that I saw Endemic fever, under the inter- 

 mittent and remittent forms, become Epidemic in an army, 

 was in the year 1794, when, after a very hot and dry summer, 

 our troops, in the month of August, took up the encampments 

 of Rosendaal and Oosterhout, in South Holland. The soil in 

 both places was a level plain of sand, with perfectly dry sur- 

 face, where no vegetation existed, or could exist, but stunted 

 heath plants : on digging, it was universally found to be per- 

 colated with water to within a few inches of the surface, which, 

 so far from being at all putrid, was perfectly potable in all the 

 wells of the camp. I returned to Holland in the year 1799, 

 with the army under the command of the Duke of York, 



which 



