Of the conditions which are ascertained to be essential to the putrefactive process of dead organic substance, whether vegetable or animal, those of heat and moisture are the most certain, and as far as we yet know, the most powerful. Accordingly, in every situation in which circumstances concur to produce great moisture, while the heat is maintained with some steadiness within a certain range, there the febrile poison is invariably generated in large quantity, and in great potency. Wherever generated, we have no means of ascertaining its existence but by the effects it produces on the human body. Now and then circumstances arise which illustrate these effects in an exceedingly striking manner. This is the case when large numbers of men, previously in a state of sound health, are simultaneously exposed to it. Examples of such occurrences, as numerous and as complete as can be desired, were long since recorded, among many others, by one very accurate observer, who is of the number (no small one) of those who have given valuable lessons to the world, which have been forgotten, and to which it is a useful labour to recall the attention of the present age. “In the beginning of June, 1742,” says Sir John Pringle, in his Observations on the Diseases of the Army, “the British troops began to embark for Flanders. There were in all, of foot and cavalry, about 16,000: the winds were favourable, the several passages short, the men landed in good health, and went into their several garrisons. The head-quarters were at Ghent. During the Summer and Autumn the weather was good, the heats moderate, and the country in general healthy. The British officers continued well, but many of the common men sickened. Ghent is situated between the high and the low division of Flanders; one part of the town called St. Peter’s Hill, is much higher than the rest, and in this, the barracks, having drains and free air, were quite dry; so that the soldiers who lay there enjoyed perfect health. But those who were quartered in the lower part of the town (mostly on the ground-floors of waste houses, unprovided with drains, and of course damp) were sickly. The battalion of the first regiment of guards was a remarkable instance of this difference of quarters. Two of the companies lay on St. Peter’s Hill; the remaining eight in the lower part of the town, in rooms so very damp, that they could scarce keep their shoes and belts from moulding. In the month of July, the sick of this battalion amounted to about 140; of which number only two men belonged to the companies on the hill, and the rest to those in the lower town.”[31]