These tainted waters may possibly act in both ways--directly, and through the medium of the air.
While on the subject of the causes or sources of disease, I may mention two which do not appear to me to have been sufficiently considered and provided against in India.

First, when a new cantonment is formed and occupied in haste, during or after a campaign, terraces are formed of the new earth dug up on the spot to elevate the dwellings of officers and soldiers from the ground, which may possibly become flooded in the rains; and over the piles of fresh earth officers commonly form wooden floors for their rooms to secure them from the damp, new earth.

Between this earth and the wooden floor a small space of a foot or two is commonly left.

The new earth, thus thrown up from places that may not have been dug or ploughed for ages, absorbs rapidly the oxygen from the air above, and gives out carbonic acid, nitrogen and hydrogen gases, which render the air above unfit for men to breathe.

This noxious air accumulates in the space below the wooden floor, and, passing through the crevices, is breathed by the officers and soldiers as they sleep.
Between the two campaigns against Nepal in 1814 and 1815, the brigade in which my regiment served formed such a cantonment at Nathpoor, on the right bank of the river Coosee.