E. Hindle 
137 
temperature of 22° 0. About a year later the surviving ticks, of 
both series, produced no infection when fed upon healthy rats. At 
certain intervals the ticks were repeatedly fed on uninfected rats but 
never produced any infection in them. Those which had been infected 
with S. duttoni were then fed upon a rat infected with the same strain 
and the following month these ticks were again fed upon a healthy 
animal, but no infection was produced. It was subsequently found 
that after being taken into the alimentary canal of an immune tick, the 
spirochaetes were rapidly destroyed and only retained their infectivity 
(determined by inoculation) for two days. The destruction of the 
parasites took place in the gut of the tick and the spirochaetes did not 
penetrate into any of its organs or tissues. 
The fact that 0. mouhata may possess an active immunity against 
the Relapsing Fever of Tropical Africa is of the highest importance 
from the epidemiological point of view, and also explains the negative 
results which have followed many of our transmission experiments. 
Introduction. 
The experiments described in the following pages are a direct 
continuation of some performed, in 1909, by Nuttall and Fantham, 
who tried to determine, by means of inoculation experiments, which 
organs of the tick harboured 8. duttoni. Owing to a succession of 
epidemics of another disease amongst the mice used in these experi¬ 
ments, the investigation was never completed, and in 1910, when I 
commenced to work on this subject, Professor Nuttall kindly placed the 
records of these unpublished experiments at my disposal. During 
the past year a number of experiments have been made in order to 
determine the mode in which the tick transmits spirochaetal infection, 
and also which organs, or tissues, harbour the parasites. 
Although the number of experiments is rather small, yet the results 
are sufficiently definite to show which organs of the tick are infective, 
and also to arrive at some conclusions regarding the influence of 
temperature upon their infectivity. The results which have been 
obtained support Leishman’s view that it is not the salivary glands but 
the gut which remains infective, and that infection is produced probably 
as a result of the excretion of infective material from the Malpighian 
tubules, which enters the oppn wound caused by the tick’s bite. 
