MICROBIAL DISEASES OF MAN AND ANIMALS. 



6 7 i 



In Central America a spirochaete, which causes a disease almost identical 

 with tick fever, is carried by Ornithodoros chinche. 



FIG. 119. Ornithodoros moubata. (Murray from Doflein.} 



Spiroch&ta duttoni is a slender organism measuring from 14^ to 16^ in length; its 

 thread-like body lies in a number of waves, which vary greatly in number, according to 

 the way in which the preparation is made; consequently, the number of waves is not a 

 constant character which can be relied upon for the identification of this species of 

 spirochaete. This spirochaete is composed of an outer ecto- 

 plasmic sheath, and of a core of chroma tin; the sheath 

 extends at either end into flagellum-like prolongations. It 

 probably has an extremely small undulating membrane. 

 Multiplication is accomplished by both transverse and lon- 

 gitudinal binary division. Sometimes, perhaps most often 

 toward the end of an attack of fever, the spirochaetes coil up 

 tightly, within a cyst-like matrix. Such encysted forms may 

 lie within red blood cells, liver cells, and spleen cells; they are 

 seen most frequently in the liver and spleen, and they are 

 always present in the alimentary canal of ticks which have 

 ingested spirochaete-infected blood. The chromatin of both 

 free and encysted spirochaetes may be fragmented, more or less 

 regularly. In the tick, cysts, containing a spirochaete with fragmented chromatin, 

 burst and set free the granules of chromatin; it is probable that each granule develops into 

 a spirochaete. It is not impossible that the same method of multiplication also occurs 

 in man. 



The form and the exact way in which the spirochaete is transmitted by the tick is 

 not known. It is probable that a tick, once infected, never loses its power to transmit 



FIG. 1 20. Spiroc- 

 hceta duttoni. (After 

 Dqflein.) 



