G. H. F. Nuttall and E. Hindle 
327 
Ex23. a. {Control.) 
On January 18, thirty of these nymphs were warmed for one night 
to a temperature of 37°C., and the following day placed on a calf and 
allowed to gorge themselves. This animal showed parasites in its blood 
thirteen days later, and died of East Coast Fever twenty-three days 
after the nymphs liad been placed on it. 
Ex^). B. Demonstrating the non-infectivity oj infective ticks 
maintained at about 10° C. for three weeks. 
- The nymphs, having thus been shown to be infected, were placed in 
the cellar on February 25 at a temperature of about 10° C. After 
having been kept at this temperature for twenty-one days (until 
March 18) 105 of these nymphs were placed, without any previous 
warning, on a calf which was kept in the cold stall at ordinary out-door 
temperatures (about 8° C.). 
The gorged nymphs dropped off five to eighteen days later, and the calf 
was kept under observation for a month (until April 1(J) during which 
period it never showed any rise in temperature nor any other symptoms 
of East Coast Fever. 
On April 16, thirty infected nymphs that had been kept at a tempera¬ 
ture of 22° C. were placed on this calf, which was still kept in the cold 
stall. After an incubation period of eleven days the calf showed a rise 
in temperature and died of East Coast Fever twenty-one days later, in 
this case the disease having a somewhat prolonged course. 
This experiment clearly shows that nymphs of R. appendiculatus 
infected with Theileria parva, after being exposed for three weeks to 
a temperature of about 10° C., lose their infectivity and become innocuous 
to cattle. 
Exp. C. Demonstrating the effect of warmth in restoring the 
infectivity of ticks j^'i’evionsly non-infective from exposure to cold. 
Having found that a low temperature causes a tick to become 
non-infective, it remained to be seen whether the infectivity could be 
restored by subsequent warming. For this purpose some of the nymphs 
from Exp. B, were again kept at a temperature of about 20° C. for 
a period of four weeks, and, finally, for two days at 30° C. Forty of 
these nymphs were then allowed to gorge themselves on a calf. Thirteen 
