In 1903, Marchoux and Salimbeni, working in Brazil, made the first detailed study of the disease, and showed that the causative organism is transmitted from fowl to fowl by the tick _Argas persicus_. They found that the ticks remained infective for at least five months. Specimens which had fed upon diseased birds in Brazil were sent to Nuttall and he promptly confirmed the experiments. Since that date many investigators, notably Balfour and Hindle, have contributed to the elucidating of the life-cycle of the parasite. Since it has been worked out more fully than has that of any of the human spirochætes, we present Hindle's diagram (fig. 143) and quote the brief summary from his preliminary paper (1911_b_). "Commencing with the ordinary parasite in the blood of the fowl, the spirochæte grows until it reaches a certain length (16-19µ) and then divides by transverse division. This process is repeated, and is probably the only method of multiplication of the parasite within the blood. When the spirochætes disappear from the circulation, some of them break up into the coccoid bodies which, however, do not usually develop in the fowl. When the spirochætes are ingested by _Argas persicus_, some of them pass through the gut wall into the cœlomic fluid. From this medium they bore their way into the cells of the various organs of the tick and there break up into a number of coccoid bodies. These intracellular forms multiply by ordinary fission in the cells of the Malpighian tubules and gonads. Some of the coccoid bodies are formed in the lumen of the gut and Malpighian tubules. The result is that some of the coccoid bodies may be present in the Malpighian secretion and excrement of an infected tick and when mixed with the coxal fluid may gain entry into another fowl by the open wound caused by the tick's bite. They then elongate and redevelop into ordinary spirochætes in the blood of the fowl, and the cycle may be repeated." [Illustration: 143. Spirochæta gallinarum. After Hindle.] Hindle's account is clear cut and circumstantial, and is quite in line with the work of Balfour, and of Leishman. Radically different is the interpretation of Marchoux and Couvy (1913). These investigators maintain that the granules localized in the Malpighian tubules in the larvæ and, in the adult, also in the ovules and the genital ducts of the male and female, are not derived from spirochætes but that they exist normally in many acariens. They interpret the supposed disassociation of the spirochæte into granules as simply the first phase, not of a process of multiplication, but of a degeneration ending in the death of the parasite. The fragmented chromatin has lost its affinity for stains, remaining always paler than that of the normal spirochætes. On the other hand, the granules of Leishman stain energetically with all the basic stains.