VARIETIES 499 



tinguished. Differences have been made out with regard to 

 clinical features, pathogenic effects, and immunity reactions. 

 Of these the last mentioned are probably the most important. 

 It has been shown, for example, by the work of Novy, Strong, 

 and Mackie, that the American spirochaete is probably a distinct 

 species, as animals immunised against it are still susceptible to 

 infection by the European and Asiatic organisms, and vice versa. 

 The relationship between the two latter is certainly closer, and 

 no distinct immunity differences have been established. Re- 

 lapsing fever in Asia is evidently a much more severe disease 

 than in Europe ; Mackie gives the mortality in Bombay at the 

 comparatively high figure of 38 per cent. But differences in this 

 respect, as well as in pathogenic effects, may simply depend on 

 variations in virulence. At present no definite statement can be 

 made on this point. 



The fact that tick fever and other spirilloses are con- 

 veyed by the bites of insects makes it extremely probable that 

 relapsing fever is transmitted in this way. At first the bed-bug 

 was believed to be the vehicle of transmission, and the experi- 

 ments of Karlinski and of Tictin, which showed that the spiro- 

 clia-tes might remain alive and virulent in the body of this 

 insect for some time after it had sucked the blood of a patient, 

 lent some support to this view. Attempts to transmit the 

 disease by means of the bites of bugs were, however, generally 

 unsuccessful ; Mackie produced the disease in only one out of 

 six monkeys used for this purpose, though large numbers of bugs, 

 which had bitten relapsing fever patients, were used. On in- 

 vestigating an epidemic of the disease, however, he obtained 

 a considerable amount of evidence on epidemiological grounds 

 that the disease was carried by the body louse. He also found 

 that the spirochaites in the blood which had been sucked under- 

 went great multiplication about three days afterwards, and 

 formed large tangled masses in the stomach contents. The 

 view that the louse is the agent of transmission of the human 

 disease is strongly supported by the experiments of Manteufel, 

 who was able to transmit infection from rat to rat in nearly 

 60 per cent, of the experiments made, whereas he obtained 

 only negative results by means of bugs. Further observations 

 are still necessary. 



African Tick Fever. 



The disease long known by this name as prevalent in Africa 

 has also been shown to be caused by a spirillum or spirocha !<. 



