Gr. H. F. Nuttall 
61 
lasted eight days, in the fifth monkey it lasted six days. Spirochaetes 
were not discoverable microscopically in the infective lice. The period of 
incubation observed in the monkeys corresponds to that observed in men 
who became infected under natural conditions. This is in marked contrast 
to what obtains when monkeys are inoculated directly with blood taken 
from cases of human relapsing fever, in the latter case the incubation 
period is always less than 24 hours 1 . 
Nicolle, Blaizot and Conseil (10. vn. 1912, pp. 1636-1638) noted the 
striking similarity in the epidemiology of typhus and relapsing fever 
as seen in North Africa. The two diseases spread in the same manner, 
occurred in the same localities, attacked the members of hospital staffs 
who were concerned with the admittance and handling of incoming 
patients with their effects, whereas the physicians and nurses who 
handled the patients after they were bathed and cleansed escaped the 
infection. 
The authors’ observations regarding the mode of infection in relapsing 
fever were most interesting. They found that when body-lice were fed 
upon infective blood, the spirochaetes disappeared rapidly from the insects ’ 
intestinal tract, but few could be detected microscopically after the 
lapse of 5-6 hours and all had disappeared after 24 hours. On the 
8-12th day, typical, active spirochaetes reappeared in the lice. At first 
the spirochaetes were short, subsequently they attained the usual 
dimensions they possess in man’s blood. They were seen to persist 
until the 19th day in the louse. A monkey was infected with the sub¬ 
stance of a louse which had been crushed 15 days after it had fed on 
infective blood. Thousands of infected lice were allowed to bite monkeys 
and a man with negative results 2 . It is clear that in nature infection 
must occur through the infective lice being crushed upon the indi¬ 
vidual. All lousy persons scratch themselves, thereby crushing vermin 
upon their bodies, and infecting the excoriated skin with contaminated 
fingers and nails. That infection occurs in this way was demonstrated 
experimentally by one of the authors upon his own person; crushed 
lice, placed upon the excoriated skin, produced relapsing fever after 
an incubation period of five days. A drop of blood containing the 
1 About this time Balfour (1911, p. 70) working in the Sudan, examined a few body- 
lice that had been taken from relapsing fever patients; he failed to infect monkeys through 
their agency and failed to keep the insects alive under experimental conditions. 
2 In one experiment a man was subjected to 6515 (later increased to 15,000) bites 
of infected lice. Further details of these experiments will be found in a later paper by 
these authors (1913, pp. 17-19, 29) and the papers of Nicolle and Blanc (1914). The 
latter record a second experiment on man wherein 1000 bites did not produce infection. 
