378 
susceptible to inoculation with S. duttoni , and vice 
versa. 
Pathology .—In animals the chief change is in the 
spleen, which is much enlarged, with haemorrhagic 
infarcts and areas of necrosis in chronic cases. There 
may be effusion into the serous cavities, and petechiae 
of the membranes. Necrotic areas occur in the liver, 
and the lymphatic glands are often haemorrhagic. 
The bone marrow is soft. 
Mode of Transmission. —This is effected by Ornitho- 
dorus moubata (p. 329) in the adult and nymphal stage, 
the latter being probably by far the most important. 
The transmission is thus hereditary. The incubation 
period from tick bites, in the case of animals, is about 
five days. Koch found from seven to fifty per cent, of 
ticks collected from native huts, infected. Koch found 
spirochaetes in about twenty-five per cent, of eggs up 
to the twentieth day of development in the ovaries 
of ticks which had sucked spirochaete blood. 
Addendum 
The spirochaete in East African tick fever is 
morphologically identical but different from S. duttoni , 
according to Fraenkel. 
3. Sp. novyi. —Uhlenhuth and Haendel have shewn, 
by means of agglutination with specific spirochaete sera, 
that the American relapsing fever is different from others. 
It is about 17/^ long by o*3/a broad, the undulations, 
six to eight in number, 1‘9/A in width. 
4. Sp. carteri (Mackie) of Bombay relapsing 
fever, the mortality of which is 38 per cent. The 
commonest forms are 10 to 1 6/a, average length 26 to 
32/A by o*5/a. Monkeys are the most susceptible, but 
according to Mackie other animals can also be infected 
at least temporarily. 
