1. An account is given of a series of experiments on calves and pigs on which
infective Hyalomma transiens were allowed to feed for periods of variable duration.
2. It was determined that the causal agent can be transmitted by the vector
as early as 72 hours, but usually between 72 and 96 hours after attachment.
3. Tick-feeding periods of three, four or five days are followed by either
inapparent infections relatively mild or severe reactions and recovery.
4. Tick-feeding periods of six days and longer are followed by severe or very
severe reactions terminating fatally in 75 per cent of cases.
5. The behaviour of the causal agent of sweating sickness does not conform
to that observed in arthropod-borne viruses.
6. It is suggested that the causal agent is a "toxin" generated by adult
ticks during the process of feeding.
7. Possible prophylactic measures based on control of the infective tick are