soil; of which they are not the aborigines.[10] [8] The Walcheren expedition. [9] Rapid changes in the barometric pressure of the atmosphere strongly affect some persons, but the _malaise_ caused does not seem to be of a permanent character. In the spring, in Britain, when north-easterly winds prevail, the amount of skin disease, rheumatism, neuralgia, &c., is sufficiently remarkable, and the blights they cause in plants is a fact known to all. In a work published by Mulder (“Water en Miht,” Amsterdam, p. 181), we find it mentioned that Van Swinden investigated the mutations of atmospheric pressure as a cause of sickness, and arrived at the conclusion that a low pressure was not the cause of sickness and fever. He remarked that although there had been many years in which much sickness prevailed, seemingly connected with hot and dry weather, the barometer had varied but little. Thus, at Haarlem, in the period between 1755 and 1780, the maximum was 30·9, the minimum or lowest, 28·0. The summer of 1779 was extremely hot, and a fever epidemic appeared which continued for three years. It was ascribed to the draining of several polders. Several learned societies made reports on the subject of this fever, but they elicited no new facts. It was generally agreed that the deeper the mud and turf containing vegetable matter were under water, the less was the sickness resulting from the draining. A Mynheer Driessen called public attention to the circumstance that on the coasts of Holland there were many places where animal and vegetable matter had accumulated and was in a state of rottenness or fermentation; and in this state he suggested that being carried inland by strong westerly winds, it might give rise to sickness. It is remarkable, however, that both the influenza and cholera progressed against the prevailing westerly winds. [10] Men in a state of nature seem to resist malaria. Thus the natives of Newfoundland and of Canada generally, and indeed of all America, withstood readily the malaria of their native land, but perished when brought within the influence of European domesticity. We must allow, however, for the power of race. On the other hand, it seems almost certain that the old Roman armies withstood the influence of climate much more effectually than modern armies do. They lived generally in camps, which they themselves fortified. Of their sanitary regulations we know nothing, but of their camps we know that no English or French soldiers could possibly stand their ground for any length of time similarly encamped. A legion (about 12,000 men) encamped on a space of 700 yards square; what became of the refuse of the camp, and how was it disposed of? No Crimean disasters ever happened to Cæsar; he could not afford to lose his veteran Legions as we lost the Guards. CHAPTER III. THE ORIENTAL PLAGUE--QUESTION OF CONTAGION.