G. H. F. Nuttall 
87 
Seasonal Variation in the Number of Lice on Man. 
On the ground that typhus is chiefly a disease which prevails in 
camps in winter, Kisskalt (13. v. 1915, p. 379) concludes that its increase 
at this season cannot depend merely upon the numerical increase of 
lice, for no seasonal variation in the number of lice was observable in 
Berlin. Several authors have sought to attribute the increase of typhus 
to a corresponding augmentation in the numbers of lice in winter. 
Beginning with the year 1909, Dr W. H. Hamer, of the London 
County Council, conducted observations upon the prevalence of fleas, 
bugs and lice in the beds and bedding of common lodging-houses. The 
population of such houses is not stationary. Hamer’s report for 1910 
(p. 7, Diagram IV) illustrates the prevalence of the insects during the 
preceding year (1909). Inspectors examined the beds in 11 districts, 
Fig. 1. Chart illustrating the variation in the percentage of louse-infested beds during 
the years 1909-1916, in London; the black columns represent the monthly records. 
The seasonal incidence is most clearly shown in 1909 and 1916. Curve constructed 
from data kindly supplied by Dr W. H. Hamer, of the London County Council. 
“ten beds being examined daily on five days out of seven making a 
total of 550 beds weekly.” The sheets of each bed were carefully 
scrutinized for lice. The louse-infested beds ranged from a maximum 
of 31 % to a minimum of 12 % in the first weeks of February and June 
respectively. The beds were found most frequently verminous in 
January-February; few were found infested in April-June, after which 
the curve gradually rose, attaining a fairly high point in August-October. 
The autumn rise appears partly attributable to the return to London, 
on the approach of winter (Sept.-Oct.), of hop-pickers who are frequently 
verminous, tramps and others coming later. 
Dr Hamer has most kindly supplied me with data relating to the 
prevalence of lice in common lodging-house beds during the years 
