90 
Biology of Pediculus liumanus 
in clothing near the surface of the body is deleterious to corporis 
is shown, for instance, by the fall in the number of eggs that hatch at 
37° C. (ea. 54 %) as compared to 30° C. (ca. 70 %) in the thermostat 
(see p. 152). 
I have, however, obtained striking evidence of the deleterious eflect 
of a slight increase of warmth on lice maintained on the person by the 
wristlet method (p. 107). Whilst raising capitis, a number of adults 
died prematurely, their early death being attributed to the advent of 
warm weather (p. 132). The heat was sufficient to cause me some dis¬ 
comfort at night. The wristlet } worn on the arm or knee, was covered 
by bedclothes and it was noticed that the adults on warm nights in¬ 
variably wandered to the chiffon beneath the lid of the box, the tem¬ 
perature near the body accompanied by slight perspiration evidently 
being unpleasant to them. The lice were found dead in the box 
especially after warm nights. The effect of the excessive warmth in 
bed not only affected the adults, it increased the mortality among the 
hatching larvae to 27 %, whereas previously the mortality had only 
been 2 %. 
Influence of Cltmate on Lice. 
Anderson and Golclberger (n. 1910, p. 183), who studied typhus 
fever in Mexico, observed cases on the Plateau at an altitude of 
1500-1800 metres or more. The disease does not occur at lower 
altitudes. On enquiry, they found that body-lice are practically 
unknown at Tampico (Coast of Gulf of Mexico, subtropical) though 
head-lice are common. This is “so well known among the natives 
that when peons from the plateau, in search of work, arrived infested 
with body-lice, they declined to take any special measures for the 
destruction of the parasites on the ground that lice could not live there 
more than a few days, and such he (Dr Rolph, the authors’ informant) 
actually found to be the case.” 
Apart from the higher temperature and increased atmospheric 
humidity prevalent at lower altitudes in Mexico, the slight rise of body 
temperature, amounting to about O5-1-0 0 C., which may occur, accord¬ 
ing to Plehn, in persons on first going from a cold to a hot country, 
may also contribute to rendering the proximity to man unpleasant, 
thus driving the lice to the outer clothing, starvation and death. This 
appears to me worth mentioning in referring to the observation above 
described. 
It would be of interest to know if similar evidence to that emanating 
