The Vectors of Relapsing Fever 527 



blood be secured during a febrile paroxysm. The readiness with 

 which the organisms take the stain leaves little to be desired. 



Novy and Knapp have found that the serum of recovered cases 

 can be used to assist in making diagnosis because of its agglutinating, 

 germicidal, and immunizing powers. 



Immuiiity. — The phenomena of immunity are vivid and im- 

 portant. At the moment of decline of the fever a powerful bacterio- 

 lytic substance appears in the blood and dissolves the organisms. 

 At the same time an immunizing substance appears. The two do 

 not appear to be the same. 



The immunizing body affords future protection to the individual 

 for an indefinite length of time. It can be increased by rapidly in- 

 jecting the animal with blood containing spirochaeta. Serum con- 

 taining the immunizing body imparts passive immunity to other 

 animals into which it is injected, and, according to Novy and Knapp, 

 estabhshes a solid basis for the prevention and cure of relapsing 

 fever in man. 



THE VECTORS OF RELAPSING FEVER 

 I. Ticks 



The ticks thus far known to act as vectors of relapsing fever are two species of 

 the genus Ornithodorus. Thirteen species of this genus are described in "A 

 Text-book of Medical Entomology," by Patton and Cragg, who give excellent 

 tables for their identification and additional valuable information is to be found 

 in the excellent "Monograph of the Ixodoidea," by Nuttall. Ornithodorus ticks 

 of various species are to be found pretty widely distributed throughout tropical 

 and semitropical regions of both hemispheres. In general, they are most numer- 

 ous where the temperature is highest and the soil driest. 



The genus Ornithodorus was described by C. L. Koch and characterized as 

 follows: "The body is flat when starving and convex when replete, and may be 

 nearly as broad anteriorly as posteriorly, or pointed and beak-like anteriorly. 

 The margin of the body is not distinct but is of a similar structure to the rest of 

 the integument which is generally mamillated. On. the ventral surface there are 

 two well-marked folds, one internal to the coxae, the cbxal fold, and the other 

 above the coxas, the supracoxal fold; there is also a transverse pre-anal groove, 

 as well as a transverse postanal groove. Eyes are either absent or present in 

 pairs on the supracoxal fold; one pair between coxae I and II, and the other 

 between coxae III and IV. 



The Ornithodorus savignyi is the transmitting agent of Spirochaeta berbera; 

 Ornithodorus moubata of Spirochaeta duttoni. 



Ornithodorus savignyi. — The description given by Patton and Cragg ("A 

 Text-book of Medfcal Entomology," 1913 p. 586) is as follows: Integument 

 leathery and covered by distinct non-contiguous mammiUas and numerous short 

 hairs mterspersed. Supracoxal folds well marked, with two eyes one each side. 

 Coxal folds less well marked. Pre-anal groove distinct. The basis capituli 

 broader than long and shorter than the rest of the rostrum. Hypostome with 

 six principal rows of teeth, the external the stoutest. Palps with first and second 

 segments of equal length, third segment the shortest. Coxae contiguous; pro- 

 tarsus and tarsus of legs I, II, and III with three well-marked humps; thejtwo 

 proximal humps on tarsus of leg IV are close to each other, while the third is 

 separated by an interval of about two and a half times the distance between the 

 first and second. 



Length 5-12 mm. Width 4-8.5 mm. The female and male resemble each 

 other except that the latter are smaller. Its genital orifice is markedly smaller. 

 In the female the genital orifice is a broad transverse slit which can be made to 

 gape and is guarded by two flaps like valves; in the male the orifice is oval and 



