326 
East Coast Fever 
eighteen ticks, similarly treated, were injected into another calf. The 
animal on which the ticks had engorged l)ecame infected after an 
incubation period of thirteen days and died of East Coast Fever fifteen 
days later. The two calves that had been inoculated with tick contents 
were kept under observation for three months, but both remained 
healthy. 
We cannot explain the negative results of the.se experiments, and 
are continuing our investigations on the subject. 
III. Experiments on the effect of cold on the infectivity of 
R. appendiculatus infected ivith Theileria parva. 
In our efforts to determine what factors influence the development 
of Theileria jxirva in the tick, our attention was at once directed towards 
the effects of low temperature. It is well known that Stegornyia fasciata 
cannot transmit Yellow Fever if the temperature falls below about 
24° C., and it might be assumed that temperature exerts a similar 
effect upon the transmission of East Coast Fever by R. appendiculatus. 
It may be noted that Theiler (1909) exposed ticks infected with 
East Coast Fever to varying degrees of cold for different periods. His 
remarks were as follows (loc. cit. p. 59):— 
“ (1) a temperature of 0° C. retards the hatching of brown ticks into 
adults, (2) a temperature of 0°C. does not interfere with the development 
of the parasite within the engorged nymphae, (3) a temperature of 
0° C. does not kill the virus contained in engorged nymphae of the 
brown tick. In no instance was any difference noted in the virulency 
of the disease; the only point of interest was that the ticks kept at 
a low temperature moulted at a later date than the controls, but when 
the former were placed on susceptible cattle these animals promptly 
contracted the disease and died.” Theiler does not give any particulars 
of his experiments, and we are unable to explain the discrepancy 
between his results and those obtained in our experiments. 
On October 30, a number of larvae of R. appendiculatus were placed 
on a calf heavily infecteil with East Coast Fever. The gorged larvae 
dropped off three to five days later and the calf died of the disease as 
the last larvae dropped off. The gorged larvae were kept in a 
greetdiouse at a temperature of about 25° C., and the infected nymphs 
began to emerge about a week later. From December 13 onwards the 
nymphs were kept at a temperature of about 19° C. These ticks were 
used iti the following experiments (A, B, C):— 
