136 
Spirocliaetosis 
published, C. Fraenkel (1907, b) also succeeded in obtaining a strain 
virulent for mice after passage through a monkey, the blood in this 
case also having been sent from Russia in a leech. 
Balfour (1911) has quite lately published in tabular form an 
extensive and carefully compiled comparative study of the human 
fevers caused in different parts of the world by the various spirochaetes 
known at the present moment. Under the heading “Animals sus¬ 
ceptible ” we are told that the Spirochaeta recurrentis is transmissible 
to small rodents, only after passage through monkeys. This is of 
course the experience of Fraenkel and also of Uhlenhuth and Haendel. 
The experiments that are now being recorded will show that the 
passage through a monkey is necessary only in order to obtain a 
“ permanent ” strain. 
In a synoptical review like Balfour’s excellent table it is of course 
impossible to draw a distinction between the course of the disease in 
Europeans and Africans as far as regards tick-fever. On the other 
hand the difference is very evident in Uganda, though there it might 
more rightly be said to be manifested in the symptoms resulting from 
different degrees of acquired immunity, according to whether the 
affected individual comes from a tick-infested counti’y or not. I have 
seen a Swahili from Mombasa and a Lendu boy from Lake Albert 
have most severe attacks, whilst Baganda would go about their usual 
occupations with numerous spirochaetes in their blood; also I have 
known Basesse to be bitten by ticks and not show any symptoms, 
though observed for a fortnight after. Of course it is possible that 
these last cases were bitten by non-infected ticks, especially since 
Kindle (1911, a) has shown that 30 “/o of the Ornithodoriis mouhnta 
from Uganda are immune to infection with S. duttoni. However, 
natives from the mainland caught tick-fever in the very same rest- 
houses and showed numerous spirochaetes in their blood nine days 
later. 
In crossing with a caravan of porters from a tick-free region to 
where the rest-houses are tick-infested, the acquisition of tick-fever 
soon makes itself manifest among the men, while the natives of a tick- 
infested region, working under the same conditions, remain unaffected. 
A certain degree of immunity can therefore be acquired to this 
disease by repeated infections, and this immunity shows itself also in 
a much milder course of the disease, in the cases where the infection 
succeeds in overcoming the natural defence of the human organism. 
AccoT'ilingly we might come to the conclusion that though the 
