This Spirochæte, which occurs in fowls and is pathogenic, is transmitted by the tick _Argas persicus_. It is about 10 µ to 20 µ long. There is a pathogenic spirochæte known to occur in geese, named by Sakharoff (1891) _S. anserina_, and found in Caucasia. This may be the same as _S. gallinarum_, in which case the name _S. anserina_ will have priority. These organisms cause fever, diarrhœa, anæmia and death. The life history of the avian pathogenic spirochætes has been studied by Balfour, by Hindle[150] and by Fantham.[151] It is essentially similar to that of _S. duttoni_. [150] _Parasitology_, iv, p. 463. [151] _Annals Trop. Med. and Parasitol._ (1911), v, p. 479. Marchoux and Couvy[152] (1913) consider that the “fragmentation of the chromatin” in spirochætes is a process of degeneration. Working with _A. persicus_ and _S. gallinarum_, they state that a large number of the spirochætes ingested by the Argas almost immediately pass through the wall of the alimentary canal and appear in the hæmocœlic fluid. Marchoux and Couvy consider that Leishman’s granules may be found in the Malpighian tubules of various Arachnids. They found spirochætes in the cephalic glands of infected Argas. They consider that spirochætes remain as wavy spirochætes within the tick, if they are to be infective, though the spirochætes may become so thin as to be invisible! The latter argument is obviously weak, and it was never asserted that all granules in the Malpighian tubules of infected ticks were derived from spirochætes. With dark-ground illumination small, refractile spirochætal granules may be seen to grow into spirochætes. The granule phase of spirochætes has recently been discussed by Fantham[153] (1914). [152] _Annales Inst. Pasteur_, xxvii, pp. 450, 620. [153] _Annals Trop. Med. and Parasitol._, viii, p. 471. *Spirochæta recurrentis*, Lebert, 1874. Syn.: _Spirochæta obermeieri_, Cohn, 1875. This organism was discovered by Obermeier (1873) in cases of relapsing fever in Berlin. Short forms 7 µ to 9 µ long, and longer (probably adult) forms, 16 µ to 19 µ, are found in the blood. The width is 0·25 µ. Parasites 12 µ or 13 µ long are often observed. The spirochæte is found in the blood during febrile attacks and relapses, but not during intervening periods. It can be inoculated into monkeys, rats and mice. It can live in the bed-bug, _Cimex lectularius_, and Nuttall has succeeded in transmitting _S. recurrentis_ from mouse to mouse by the bites of the same bug. The French investigators Sergent and Foley (1908–9) in Algeria, and Nicolle, Blaizot and Conseil (1912) in Tunis, have shown experimentally that _S. recurrentis_ (var. _berbera_) is transmitted by lice. The latter workers also demonstrated the method of infection that commonly occurs, namely, by the scratching of the skin and crushing of lice containing spirochætes on the excoriated surface of the body.