In this way, not only are the sites and the vicinity of the huts and tents kept comparatively dry, but the surface water is morereadily removed, the exhalations from the damp soil diminished, and the air purified. The experience of the army in the Crimea showed the very beneficial effects of this surface drainage and trenching on the health of the troops. Dampness of the air, arising from the nature of the locality , proceeds from the topographical peculiarities of the ground preventing a free circulation of the air, and the atmosphere becoming stagnant, and charged with moisture and emanations from the ground. The valley of Karani above Kadikoi afforded an illustration of this, in certain states of the weather. It was observed in other parts of the seat of the war in the East, that damp white mists, settling in valleys or hollows occupied by troops, had been the precursors of epidemic diseases, especially of cholera.
All valleys are at times exposed to similar occurances, especially such as contain stagnant lakes.
An unhealthy and stagnant state of the air is sometimes increased by brushwood or trees. The evils resulting from these local causes of dampness were not unfrequently aggravated by the manner of pitching tents and erecting huts. Want of due preparation of the ground and defective drainage of the site, often led to 5 a damp state of the air within huts and tents, and induced a tendency to fevers. Deep trenching round the tent-site, as already mentioned, is the best remedy, and in the case of huts, the site should be isolated from the surrounding ground, and the area to be occupied by the hut, drained by a trench dug round it at least a foot below the level of the floor. If it be not practicable to drain the subsoil, and if the position must be held, adequate provision should be made with any materials at hand for raising the beds of the men above the ground.