On the life-cycle of Spirochaetagallinarum

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Abstract
The life-cycle of S. gallinarum may be briefly summarised as follows:Commencing with the ordinary parasite in the blood of the fowl, the spirochaete grows until it reaches a certain length (16 μ–19 μ) and then divides by the peculiar mode of transverse division described above. This process is repeated and is probably the only method of multiplication of the parasite within the blood. When the spirochaetes disappear from the circulation some of them break up into coccoid bodies which, however, do not usually redevelop in the fowl. When the spirochaetes are ingested by Argas persicus, some of them pass through the gut wall into the coelomic 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 spirochaetes in the blood of the fowl, and the cycle may be repeated.
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