Mode of Infection 499 



infectious agent passes to a new generation of the lice, which are 

 also infective. They also studied a tick, Ornithodorus savignyi, 

 found in those countries, thinking that it might behave like Ornith- 

 odorus moubata toward Spirochaeta duttoni, and found that it 

 could transmit the spirochaete of the Tripolitan relapsing fever, 

 though apparently not that of the Tunisian fever. 



When we come to consider Spirochaeta duttoni, however, we find 

 our knowledge much further advanced. On Nov. 26, 1904, Dutton 

 and Todd announced that they had discovered a spirillum to be 

 the specific agent in the causation of tick fever in the Congo, and on 

 the same date Ross and Milne* published the same fact. Dutton 

 and Todd subsequently withdrew their claim to priority of the 

 discovery. On Feb. 4, 1905, Ross published in the " British Medical 

 Journal" the following cablegram from Dutton and Todd, then 

 working on the Congo: " Spirilla cause human tick fever; naturally 

 infected ornithodorus infect monkey." It was not until Nov. n, 

 1905, that the paper upon the subject was read and published in 

 the same journal by Dutton and Todd, and the etiology of the dis- 

 ease made clear. These observers found that the horse-tick, 

 Ornithodorus moubata (Murray) is the intermediate host of the 

 spirilla or spirochaeta causing the disease, and that when these ticks 

 were permitted to bite infected human beings, and then subsequently 

 transferred to monkeys, the latter sickened with the typical infection. 



The matter received confirmation and addition through the studies 

 of Koch,f who studied the ticks, observed the distribution of the 

 micro-organisms in their bodies, and found that they collected in 

 large numbers in the ovaries, so that the eggs were commonly in- 

 fected and the embryo hexapod ticks hatched from them were in- 

 fective. Not only is this second generation of ticks infected, but 

 Moller has found the third generation also infected by the spiro- 

 chaeta, and it is not improbable that the infection is kept on passing 

 from female to offspring through many generations. Leishman, 

 who followed the spirochaeta throughout the body of the tick, 

 observed that it entered the ovaries and appeared in the ova in the 

 spiral form, but that in the ova it not infrequently became trans- 

 formed to "coccoid" granules which held together more or less 

 closely like tiny streptococci. He supposed that it was in the 

 granular form that the micro-organism found its way into the embryo 

 and so infected the developing nymph. There is reason to believe 

 that this was an error and that the spirals alone are the sources of 

 transmission and infection. What is true of the tick seems to be 

 equally true of the lice, the infective micro-organisms being passed 

 down from generation to generation. Thus, in regard to Spirochaeta 

 duttoni we are able to say quite definitely that the tick is the usual 

 if not the only means of dissemination. How the ticks and lice 



* "British Medical Journal," Nov. 26, 1904. 

 t" Berliner klin. Wochenschrift," Feb. 12, 1906. 



