Ross and Milne, in 1904, found that African tick fever was a spirillar fever while Dutton and Todd established the fact of its transmission by ticks. =Geographical Distribution.=—Relapsing fever was epidemic in the U. S. in 1869, since which time it has not reappeared. There have been many epidemics in Ireland, Russia, Turkey and other parts of Europe. It was a disease of importance during the Balkan War of 1912-1913. China and India have frequently been visited by epidemics as well as the Philippine Islands and the Dutch East Indies. Uganda, Congo State and German East Africa, as well as Egypt and Algeria, are important centers. There is also a relapsing fever of Colombia and Central America. ETIOLOGY AND EPIDEMIOLOGY =Etiology.=—Relapsing fevers are caused by organisms generally considered as protozoal in their nature and belonging to the flagellates. [Illustration: FIG. 36.—Spirochaetes of relapsing fever from blood of man. (Kolle and Wassermann.)] _Transmission by the tick._—The generic name _Spiroschaudinnia_ is preferred by some to the more commonly accepted _Spirochaeta_. Recently, authorities give these organisms the name _Spironema_. East and West African relapsing fever, or tick fever, is caused by _Spironema duttoni_ and the transmission is through the bite of an argasine tick, _Ornithodoros moubata_. Not only does the tick itself become infected by the taking in of blood-containing spirochaetes but likewise transmits the infection to its progeny. Leishman considers that when the spirochaetes are taken into the alimentary tract of the tick there is a breaking up of the spirochaetes into small granules which reach the Malpighian tubules. They also invade the ovary and the ova. It was thought that these granules were the infecting agents and that they were excreted in the fluid of the coxal glands or passed out with the faeces. More recently it has been claimed that these granules have no relation to the infection, which is due to spirochaetes as such. It may be stated that spirochaetes as such may be found in the secretion of the coxal glands as well as in the faeces. This coxal fluid dilutes the thick faeces and makes an emulsion which is smeared out by the body of the tick in the area of the bite puncture. [Illustration: FIG. 37.—_Spirochaeta novyi._ (Todd.)]