7(5 
Lice and Disease 
Germany, Russia and Serbia) proves that lice are constantly present 
on infected persons. These remarks apply equally to typhus, which, 
as already stated, may coexist with relapsing fever in epidemic form. 
Judging from the accessible records, relapsing fever appears to be 
somewhat more restricted than typhus in its geographical distribution. 
It has been conclusively demonstrated by carefully conducted experi¬ 
ments that Pediculus humanus serves as a carrier of Spirochaeta 
recurrentis the causative agent, from man to man 1 . 
When lice imbibe infected blood, the spirochaetes disappear rapidly 
from their alimentary canal and are not discoverable even by the 
ultra-microscope for a period of about 2-6 days after the insects have fed. 
The spirochaetes reappear in the coelomic fluid of the lice usually on 
the 8-9th day. They at first appear small, but, as time proceeds, they 
attain the dimensions and appearance they possess in human blood 
during the attack. When lice feed on infective blood, the number of 
insects that become infected with spirochaetes ranges from 10 to 42 %. 
The spirochaetes are hereditarily transmitted in the louse, for the off¬ 
spring of an infected female has been shown to be infective. This 
persistence of the spirochaetes in the louse no doubt serves to maintain 
them in nature. It has only been through the successful raising of lice 
under laboratory conditions, coupled with the use of monkeys and 
occasionally man for infection experiments, that it has been possible 
to demonstrate the phenomena herein described. 
Although lice may be infective for a few hours after they feed on 
relapsing fever blood, it is probable that infection will rarely occur by 
their transference from man to man soon after feeding. When a louse 
has fed, it usually remains quiet, whilst digesting its meal. When 
lice have hungered for any length of time, as we have frequently observed, 
they feed to excess and take a longer time to digest the large amount 
of blood imbibed. If such lice are kept cold the process of digestion is 
impeded, and I have no doubt that any spirochaetes which they may 
harbour will remain virulent for longer periods’, as I found was the case 
in bugs (see footnote 2, p. 60). How long gorged lice may remain 
infective at a low temperature remains to be determined. The experi¬ 
ments herein recorded point, however, to a rapid loss of infectivity in 
1 Topfer (31. x. 1916, p. 1571) lias the temerity to state that the work of Sergent, 
Nicolle, and their colleagues, is not “einwandsfrei.” He then proceeds to repeat their 
work. A few comparatively trivial experiments are described which are merely con¬ 
firmatory, but in his opinion (!) afford the first demonstration that lice convey relapsing 
fever. Topfer’s behaviour in this matter, flatly speaking, is thoroughly dishonest. 
