E. Hindle 
153 
as the result of an examination of lice collected from prisoners of war at 
Rennes, found Rickettsia in 53 out of 72 body-lice, whilst 27 head-lice were 
examined with negative results. Da Rocha Lima (1917) found similar organ¬ 
isms in lice collected from persons in Yolhynia, but he remarks that they only 
occurred very sparingly and were confined to the lumen of the alimentary 
canal, only rarely invading the epithelial cells. To this organism he gave the 
name Rickettsia pediculi, and used the latter character to distinguish it from 
R. prowazeki, in which invasion of the epithelial cells is the usual occurrence. 
Various other Continental observers have also recorded the finding of Rickettsia 
in lice collected from persons who had not suffered from either typhus or 
trench fever. On the other hand Arkwright, Bacot and Duncan (1919), as the 
result of a careful examination of 245 specimens reared in the laboratory, 
found only one louse infected with Rickettsia. 
Through the kindness of Mr Bacot I obtained a number of lice from the 
same stock that had been used in their experiments. These lice for many 
generations, extending back for more than three years, had been fed on a 
healthy person and had never produced any infection. 
At the Quick Laboratory these lice were fed twice daily in the manner 
described by Nuttall (1917), on a laboratory attendant who had never been 
exposed to the possibility of infection with either typhus or trench fever. 
When not in use the lice were kept in an incubator at 30° C. As a louse 
completes its life cycle in a period of less than a month, the stock used had 
been fed on healthy persons for at least forty generations. The faeces from 
these lice were examined at frequent intervals during a period of four months, 
but on only two occasions were any Rickettsia bodies found present. In addi¬ 
tion the gut contents of 420 lice were examined by making smears, and staining 
with Giemsa in the usual way. 
In the case of two individuals, bodies resembling Rickettsia were found, 
but the examination of the remainder was uniformly negative. 
In addition 112 lice from various other sources were examined without 
finding-any of these bodies. 
The results of this examination of uninfected lice are in complete agree¬ 
ment with those obtained by Arkwright, Bacot and Duncan (1919), and by 
Wolbach, Todd and Palfrey (1920) in Poland. Only two naturally infected 
lice were found in 532, and therefore it is evident that this strain of lice is 
practically free from Rickettsia infection. The positive results obtained by 
Continental observers may be explained on two hypotheses. 
(1) That owing to the prevalence of typhus and trench fever on the Con¬ 
tinent during the war, the lice had become infected with Rickettsia by feeding 
on patients suffering from these diseases; and (2) that there is a species of 
Rickettsia which lives in the alimentary canal of the louse and is non-patho- 
genic to man. 
Although the above-mentioned results would seem to favour the first 
hypothesis, it is difficult to explain all the positive results on the supposition 
