E. Hindle 
189 
in the south. Within a few years it spread up along the river Zambesi 
as far inland as Sescheke, above the Victoria Falls; and from Tete to 
Nyasaland, which is now heavily infected. It is known that the Arab 
trade route runs from Tete to Lake Nyasa and along the west side 
of the lake before going inland to Lake Tanganyika. In the Congo 
the disease occurs only along the Arab trade routes and especially 
in the places, e.g. Nyangwe, Kasonga, etc., which were used as head¬ 
quarters. Dutton and Todd found that in the Congo 0. mouhata 
collected only a short distance away from the Arab trade routes were 
uninfected, thus indicating that the disease has only recently been in¬ 
troduced into the Congo along the lines of travel and has not yet had 
time to spread into the surrounding country, as it has done in German 
East Africa. 
The way in which the disease has been introduced into Portuguese 
East Africa is not quite so clear but is probably the result of caravans 
from Tanganyika carrying infected ticks with them and thus establishing 
the disease wherever these escaped. 
With the increased facilities for communication from one state 
to another, combined with the ease with which 0. mouhata may be 
carried in bedding, clothes, etc., it seems extremely probable that the 
RelajDsing Fever of Tropical Africa will soon extend into all parts where 
the tick occurs. 
In the following table is given a list of the places from which this 
disease has been recorded, together with the date of the record and the 
name of the observer. 
Aetiology and Pathology. As mentioned above the Relapsing Fever 
of Tropical Africa is caused by the presence of S. duttoni in the 
blood of the infected patient. The disease is carried from man to 
man by the human tick, 0. mouhata, and as far as we know, by no 
other means, the tick producing infection through the excretion of 
infective material from the gut, which enters the open wound caused 
by the tick’s bite (Leishman, 1910; Hindle, 1911). The morphology of 
the parasite together with its life-history in the tick will be reserved 
for a future communication. The mechanism of transmission, together 
with all the literature on the subject, has been described in a previous 
paper (Hindle, 1911). 
Symptoms. In man, the incubation period after the tick’s bite is 
usually about a week, but may be prolonged to ten or eleven days. It 
is believed by some of the natives that when the bite is followed by 
severe local effects, sucL as inflammation and swelling, the patient 
