Gr. H. F. Nuttall and E. PIindle 
325 
Exp. 5. Deviomtrating that preliminm'y feeding of infected ticks for 
hvo days, followed by starvation for seventeen days, renders them 
non-infective. 
The partially engorged ticks that had been removed from the 
calves in the two previous experiments (3 and 4) were kept at room 
temperature (about 20° C.), those from Exp. 3 for eighteen days and 
th ose from Exp. 4 for fifteen days, after being taken from the calves. 
Then both lots were kept overnight at 37° C. and placed on a calf. 
Onl}' six nymphs were left alive, and these were allowed to engorge on 
the calf. This animal was kept under observation for four weeks during 
which period it never showed any rise in temperature. It was then 
proved to be susceptible to East Coast Fever by allowing 40 infected 
nymphs to feed upon it. After a normal incubation period the animal 
fell ill, and died from the disease twenty-seven days after the ticks had 
been applied. 
Although the number of ticks (six) used in this experiment is rather 
small, Theiler, Gonder and other observers, are all agreed that practically 
100 "/o of R- appendiculatus become infected when fed on an infected 
animal. Therefore, it seems that ticks lose their infection within 
seventeen days of ingesting blood, and we are led to assume that the 
developmental processes started by the ingestion of blood into the tick, 
continue, even if the latter is removed from its host prior to being fully 
engorged. Apparently, however, when once started, tliis development 
of the parasite results in its own destruction, unless it is able to enter 
the blood of a bovine animal within a pei’ind certainly less than 
seventeen days. 
II. Inoculation experwients 'ivith emulsions of infected ticks. 
Since our experiments showed that ticks are non-infective. until 
after they have fed for more than two days, it appeared reasonable 
to suppose that the reason why all attempts to infect cattle by the 
inoculation of ticks had hitherto failed was owing to the parasites 
having been inoculated when they were not at a suitable stage of 
development. Therefore, the following inoculation experiments were 
performed:— 
On May 14, forty infected nymphs were placed on a calf. Five days 
later thirty-seven ticks were removed from the animal and divided into 
two lots. The total contents of nineteen of these gorged ticks, emulsified 
in 0’6®/o saline, were injected into one calf, whilst the salivary glands of 
