Ct. H. F. Nuttall and F. Hindle 
323 
days later. From February 20 onwards the nymphs were kept at 
a temperature of about 20° C. These infected nymphs were used in 
all the following experiments, with the exception of A, B, and C. 
Exp. 1. {Control.) 
In order to test their infectivity, on March 4 fifty of these nymphs 
were placed on a large calf, which was kept in a heated stall at a 
temperature of about 16° C. Ten days later the calf showed a rise 
in temperature and after another five days parasites were first seen 
in the peripheral blood. The animal died of East Coast Fever on 
Maa'ch 31, twenty-seven days after the infected nymphs had been 
placed on it. 
Exp. 2. Demonstrating the infectivity of ticks after preliminary 
feeding on a rabbit for three days. 
On March 4, numerous nymphs were placed on a rabbit which was 
kept at a temperature of about 20° C. Three days later, 140 of these 
partially engorged ticks wei’e pulled off the rabbit and placed on a calf. 
The ticks at once attached themselves to the second host. Ten days 
later the calf showed a rise in temperature, parasites being first seen 
four to five days later. The calf died of East Coast Fever on April 3, 
twenty-seven days after the partially fed nymphs had been placed on it. 
It is noteworthy that, in this case, the incubation period is identical 
with that of the control animal (Exp. 1), the preliminary feeding on a 
rabbit for three days apparently having had no effect either on the 
infectivity of the ticks or on the incubation period of the disease. 
Exp. 3. Demonstrating that ticks are non-infective during the 
first two days after their becoming attached to a host. 
On April 9, fifteen infected nymphs, kept overnight at 30° C., were 
placed on the ear of a calf. Two days later the partially fed ticks 
were all removed from the animal (see below, Exp. 5). The calf was 
under observation for five weeks and daily records of its temperature 
were kept, but the animal never showed fever or any other signs of 
infection. 
In order to determine whether this calf was immune to East Coast 
Fever, on May 14 forty infected nymphs (belonging to the same lot of 
