_Cause._—The organism is unknown, presumably being too small to be seen by the highest powers of the microscope, but it is known to be transmitted by what are called sand-flies or pappataci flies, tiny and very hairy midges which breed in such places as heaps of damp stones, bricks, and tiles, cracks in surface soil, the walls of old cellars, cracks and fissures in embankments. These little flies, which sally forth upon the blood quest towards evening, are voracious blood-suckers, and feed principally in the gloaming and at dawn. They chiefly attack the wrists and ankles, and can easily bite through thin socks or light cotton or linen clothing. It has been proved that the bite of one infected fly can convey fever. During the day they hide in dark places, and may be found in the dark corners of rooms. Their bites are painful, and when numerous the bitten part may swell badly. An attack by many flies effectually banishes sleep. _Symptoms._—The fever is short and sharp—indeed, it is often called the three-day fever. The incubation period is four to seven days, and the attack is sudden, beginning with chilly sensations and a tired feeling. There may be rigors, but these are never so severe as the shivering fits of malaria. The patient becomes giddy, has a severe frontal headache with pain at the back of the eyes and pains in the back and legs. The condition, indeed, is very like an influenzal attack except that there is, as a rule, no coryza. The face is flushed and the eyes may be injected. When the latter is the case one can understand how the disease was originally given the name of the “dog disease,” as the appearance of the injected conjunctivæ resembles that sometimes seen in mastiffs and bloodhounds. There may be some sore throat, and sometimes there is a little eruption on the throat or palate. The temperature rises rapidly and may attain 103° F. It remains up for about twenty-four hours and then begins to fall, usually becoming normal on the third or fourth day. Sometimes there is a secondary rise of temperature. The patient may speedily recover or convalescence may be tedious, and the condition is sometimes followed by mental depression and the digestion may be upset. The fever is apparently never fatal but it is troublesome and debilitating. _Prophylaxis._—Protect from the bites of sand-flies. This is best done by the use of a fine-mesh net containing twenty-two holes to the linear inch. It should be of the same general pattern as the net recommended under malaria (_see_ p. 206). Tobacco smoke keeps the flies away to some extent and repellents are useful, especially vermijelli, containing some oil of citronella, the preparation known as Sketofax, oil of cassia and oil of eucalyptus. A lump of camphor as a bed-fellow is also useful as the flies dislike its odour. The patient should always be placed under a fine-mesh net to prevent his being a source of infection to others.