G. H. F. Nuttall 
267 
of ticks which become infected, as noted by Miss Muriel Robertson for 
Trypanosoma gambiense in Glossina palpalis, to which reference will be 
made in the next lecture. Such a condition might well account for some 
of the immunity which is stated to occur. We know that there are 
marked variations in the viability of spirochaetes in relapsing fever 
blood preserved in vitro. Thus, Novy and Knapp (1906) found that 
S. 7'ecurrentis (American strain) survived for 30 to 40 days in defibri- 
nated blood drawn from a rat during the onset of the disease, whereas 
they only survived 24 hours in blood drawn during the decline. 
Although Dutton and Todd, Balfour, and others observed the breaking 
up of spirochaetes into minute granules in the body of ticks, Leishman 
was the first to follow the process more clearly. He proved that the 
coxal secretion was anti-coagulant and non-infective, and that the excreta 
were infective by inoculating them into animals. He found that only 
when mouhata voided excreta in the act of biting that animals under 
experiment became infected. He therefore concluded that the mode of 
infection is contaminative through the tick’s excreta and not active 
through its proboscis. Experiments which I carried out, and which 
were extended and reported upon by Hindle in my laboratory, com¬ 
pletely confirm the results of Leishman, If the internal organs of an 
infected mouhata are carefully dissected out and well washed in sterile 
salt solution, it is found that the gut, together with its contents, the 
malpighian tubes, the sexual organs and excrement are infective when 
emulsified and injected into a susceptible animal. The coxal secretion 
always, and the salivary glands in most cases, give negative results. 
The few positive results with salivary gland inoculations may well be 
refei’red to experimental error, in that the glands, in the process of 
dissection, may easily become contaminated by spirochaetes derived 
from other organs and be imperfectly cleansed in the process of washing. 
Inoculations with emulsified eggs of moubata have also given positive 
results as might be expected, for spirochaetes have been found in them 
by a number of authors; Koch (1905) and Carter (1907) being among 
the first to demonstrate their presence in this situation. 
After being ingested by the tick, the spirochaetes usually disappear 
from the lumen of the gut in about nine to ten days, but they reappear 
if the tick is placed at 35° C. They are then found in the coelomic 
fluid and their subsequent behaviour is similar to that described in the 
fowl spirochaete. 
It is highly probable that other species of Ornithodorus play a like 
part in the etiology of relapsing fever in other parts of the world than 
