328 
East Coast Fever 
days after this animal showed its first rise in temperature and fifteen 
days later died of East Coast Fever. 
It seems, therefore, that the effect of cooling ticks infected with 
Tlieileria jmrva is to cause the parasite to become incapable of completing 
its development when the tick feeds. The parasite is not destroyed by 
the low temperature, as evidenced by the ticks again becoming infective 
on being re-heated to 20° C. This non-infectivity of R. appendiculutus 
at low temperatures resembles closely that of Argus persicus infected 
with Spirochaeta gallinaruia, for, as shown by BoiTel and Marchoux 
(1905), when infected Argas are kept at low temperatures they cease to 
be infective, but on again heating the ticks to a temperature of 35° C. 
they recover their infectivity. 
Summary. 
The foregoing experiments on the transmission of East Coast Fever 
by Rliipicephalus appendiculatiis appear to permit of the following 
conclusions: 
1. Infected ticks do not produce infection during the first two days 
when ieeding on cattle. 
2. Infected ticks are .still infective after feeding upon a rabbit for 
three days. 
3. Heating infected ticks to 37°C. for three days does not render them 
infective during the first two days after they become attached to the host. 
4. The partial feeding of infected ticks for two days, followed by 
starvation for seventeen days, renders them non-infective. 
5. Inoculations of emulsions of infective ticks collected from cattle 
on the fifth day of engorgement failed to produce infection. 
6. Infective ticks are rendered non-infective by exposure to a 
temperature of about 10° C. for three weeks. 
7. Their infectivity may be restored by subsequently warming them. 
By way of a working hypothesis, we assume that the final develop¬ 
ment of the parasite in the tick, resulting in the latter becoming 
infective, only commences after the tick has begun to ingest blood. 
Although our investigations are still in progress, we consider them 
of sufficient interest to warrant their publication at this stage. 
