544 PRACTICE OF PHYSIC. 



ation is so considerable. Dr. Lind, therefore, finds it advisable 

 for people in warm countries to have their habitations upon dry 

 grounds ; but if that is not attainable, he recommends them to 

 go aboard a ship. I once passed six months in a warm climate, 

 in the harbour of Portobello, and I observed that the men who 

 lay aboard the ships contracted no fever nor flux; whereas those 

 who went ashore, and lay for a single night there, were attacked 

 with the one or the other of these diseases. These effluvia, then, 

 do not arise from pure moisture, but seem to be connected with 

 a particular moisture arising from the earth. When the impur- 

 ities of the ground are entirely covered with water, such exhala- 

 tions are either not formed, or they are absorbed and rendered 

 innocent by the incumbent water. We have an example of this 

 in Egypt, where, from the time that the waters of the Nile 

 recede, in consequence of which a certain mud is left, the 

 Typhus JSgyptiacus arises and continues, till again, at the 

 returning season, the Nile rises to a certain height, and over- 

 flows the ground, when the disease disappears, though this in- 

 undation happens at the warmest season of the year. In like 

 manner, Senac informs us of a town in Germany, surrounded by 

 a considerable lake, where no disease was produced when there 

 was an entire surface of water; but by length of time, some part 

 of the filthy sediment emerging, the exhalation from it came 

 to be of the same nature with that from every other marshy 

 ground, and produced tertians, and other intermittents." 



LXXXV. It has now been rendered probable, that the re- 

 mote causes of fevers (VIII.) are chiefly contagions or mias- 

 mata, and neither of them of great variety. We have supposed 

 that miasmata are the cause of intermittents, and contagions the 

 cause of continued fevers strictly so named ; but we cannot with 

 propriety employ these general terms. For, as the cause of 

 continued fevers may arise from fomites, and may, in such cases, 

 be called a miasma ; and as other miasmata may also produce 

 contagious diseases, it will be proper to distinguish the causes 

 of fevers, by using the terms Human or Marsh Effluvia, rather 

 than the general ones of Contagion or Miasma. 



" It is a very curious, but at the same time a difficult problem, 

 to determine in what cases Contagion or Miasma does or does not 

 act. It certainly happens, that during the prevalence of Epidemics, 



