All infectious diseases may spread in consequence of war and develop into epidemics of varying extent. In the next chapter we shall see how the wars at the end of the fifteenth century favoured the spread of an epidemic of syphilis. In the Union Army, during the American Civil War of 1861–5, both measles and typhoid fever were very widespread, and together they were the cause of 4,246 deaths, or about 1·75 per cent of the total enlistment. Scarlet fever, influenza, yellow fever, relapsing fever, and malaria (if the war is waged in countries where this disease is endemic—especially in the Lower Danube region, in the Netherlands, Spain, and Italy) have also played an important rôle in many wars. But we give the name ‘war pestilences’ only to those infectious diseases which in the course of centuries have usually followed at the heels of belligerent armies, such as typhus fever, bubonic plague, cholera, typhoid fever, dysentery, and small-pox; we may also include here scurvy, the etiology of which has not yet been definitely determined. 1. _Typhus fever_ (spotted fever, exanthematic typhus—called in France and England simply typhus, in Spain tabardillo[2]—formerly called contagious typhus, hunger typhus, camp fever, and Hungarian fever) is an acute infectious disease of cyclic recurrence, which resembles typhoid fever only in name. From the eighth to the tenth day after infection, often somewhat sooner or later, it begins with a chill, accompanied by nausea, vomiting, violent headache, and psychic depression. In the first few days the patient’s temperature rises rapidly, and on the fourth or fifth day a rash in the form of dull-red spots, as large as a pea, breaks out over the entire body. These spots gradually grow larger, and after two or three days, through the appearance of very small haemorrhages, change into petechiae. The apathy of which the patient first gave evidence now gives way to wild delirium. At the end of the second week the temperature falls rapidly, and in one or two days becomes normal; often, however, the fall of temperature takes from six to eight days. The duration of the entire disease, accordingly, is from two to two and a half weeks. Death usually occurs at the crisis of the disease—from the tenth to the twelfth day—rarely between the sixth and ninth days or after the twelfth.