But besides the obvious and sensible qualities of the air above mentioned, there are certain obscure properties which we do not understand, and which we find difficult to investigate; for there are diseases prevailing in certain places which seem to depend on some latent state of the air. Of this kind is the complaint of the liver, so common in the East Indies, yet almost entirely unknown in the West Indies; and in the West Indies there are certain diseases which prevail in one island and not in another; such as the _elephantiasis_[41] of Barbadoes, which is an affection of the lymphatics peculiar to that island. In the climates of Europe there are also certain obscure conditions of the air that favour one epidemic more than another, and in some years more than others[42]. All this is very mysterious to us; and although we could detect these properties of the air, we probably could not prevent their bad effects, since man must every where breathe the air, whatever its qualities may be. SECT. II. Of FOUL AIR from the Neglect of Cleanliness in Men’s Persons--INFECTION. Nature has wisely so contrived our senses and instincts, that the neglect of cleanliness renders a person loathsome and offensive to himself and others, thereby guarding against those fatal diseases that arise from bodily filth. The noxious air we speak of is generated by men keeping the same clothes too long in contact with the body, while they are at the same time confined and crowded in small and ill-ventilated apartments. Such is the origin of the jail fever, otherwise called the ship and hospital fever; and it seems to be with reason that Dr. Cullen ascribes the low, nervous fever of Britain to a similar origin, being caused, as he thinks, by an infection of a milder kind, arising in the clothes and houses of the poor, who, from slovenliness or indigence, neglect to change their linen, and air their houses. Man is evidently more subject to disease than any other species of the animal creation, owing partly to the natural feebleness of his frame, but still more perhaps to the artificial modes of life which his reason leads him to adopt. There is no circumstance of this kind by which health is more affected than by clothing. Some of the most fatal and pestilential diseases are produced and communicated by it; for we see that the greater number of fevers, particularly those of the low and malignant sort, may be traced to the want of personal cleanliness.