Next to want of cleanliness, the circumstances most apt to give rise to infection are, close air and crowding. A certain length of time is necessary, in order that these should have this effect, and the longer they take place, the more certainly will infection be produced, and it will be the more virulent[50]. In order to admit air freely, the ports should be kept open whenever the weather will permit this to be done. The great objection to free ventilation is the danger of exposing men to the air in cold climates. But it fortunately happens, that fire, while it is the most effectual means of counteracting the cold air, is also the best means of promoting ventilation; for wherever there is fire, there is a constant change of air taking place by means of the draught to which it gives occasion. This cannot be done with safety and convenience in all parts of the ship; but frequent fires in the lower parts of a ship will prove extremely salutary by drying up the moisture, and producing a change of air, and also in a cold climate by the warmth it produces. The hammocks and bedding should also be aired by exposing them upon deck, especially after the ports have been long shut in consequence of bad weather. They cannot be thoroughly aired unless they are unlashed; and as this could not be conveniently done daily in men of war, it might be done from time to time by the different divisions in rotation[51]. When the men come to sleep upon them after these operations, they experience the same agreeable sensations as from a change of linen; and this must conduce to health as well as pleasure, like all other natural and moderate gratifications. It may be farther remarked in favour of cleanliness, that it is not only directly conducive to health, but is naturally connected with habits of good order, sobriety, and other virtues. The most cleanly men are always the most decent and honest, and the most slovenly and dirty are the most vicious and irregular. A ship of war must have a much greater number of men on board than what are necessary to navigate her; for, besides the marines, a great many hands are necessary to man the great guns in time of action. For this reason, there is a greater risque of the inconveniences of overcrowding than in ships intended for commerce, and therefore much greater attention is necessary with regard to ventilation and cleanliness. There is a piece of management which tends also in some measure to obviate the necessity of crowding. This is to berth the watches alternately, by which it is meant, that one half of each watch should lie on different sides, whereby they do not sleep so close, and are not so much exposed to each other’s breath and to the heat and effluvia of each other’s bodies. This has the farther advantage of preserving the trim of the ship.