There are few subjects more mysterious and difficult of investigation than this of infection. The origin of specific contagions, such as the small pox and the venereal disease, seems to be almost beyond the reach of a conjecture; and why all the contagions we know, excepting that of the bite of a mad dog, should be confined to one species of animal, their effects not being communicable to any other, is equally unaccountable. Why is the body incapable of being affected more than once by certain morbid poisons; and whence comes the striking and curious differences of susceptibility to infection in different individuals at the same time, and of the same individual at different times? It would appear that the infection of fever, which we are chiefly to consider here, does not, like some of the diseases above mentioned, depend on the continued propagation of a certain poison, but that it may spontaneously arise from a concurrence of circumstances, producing a long stagnation of the effluvia of the body on the clothes, for want of clean linen, while people are excluded from the free air, as in jails, hospitals, or ships. In order, therefore, to preserve the crews of ships from such diseases, means should be taken not only to prevent the introduction of infection already existing, but to prevent the generation of it on board. 1. Means of preventing the Introduction of Infection. War being a state of violence and confusion, in which the hurry and emergency of service may be such as to render it impossible to put in practice all the rules which might be laid down concerning the preservation of health, yet it is necessary that those who direct the navy, either in a civil or military capacity, should be aware of the causes of sickness and mortality, in order to guard against them as far as is practicable. From an indolent acquiescence in this idea of the hardships and inconveniences of war being unavoidable, I have known neglect to arise in the conduct of officers with regard to those under their command, as if it was not the duty of a commander to employ his utmost attention to alleviate the misfortunes and mitigate the sufferings of his fellow creatures; and we have seen that much more of the calamities of war arise from disease than from the sword. The like excuse might be framed for the neglect of stores and arms, which, the hurry of service might equally expose to injury. We see, indeed, infinite pains taken to prevent cordage from rotting, and arms from rusting; but however precious these may be as the necessary resources of war, it will not be disputed that the lives of men are still more so; yet, though there is the additional inducement of humanity to watch over the health of men, I do not think that this, in general, is studied with a degree of attention equal to what is bestowed on some inanimate objects.