200 
Biology of Pecliculus humanus 
on the side (a) where the black faced the sun, after 15 and 30 minutes' exposure, 
but 3 lice were found, 51 having wandered to side ( b) where the white faced the 
sun. Thermometers placed beneath (a) and (6) registered respectively 47° and 
41 C. In short the heat absorbed by the black cloth became intolerable, and 
the lice had fled to the cooler half of the mat. 
When the temperature beneath the mat fell, owing to clouds masking the 
sun, the two thermometers recording but 24° and 28° or 30° and 33° C. 
respectively, the lice showed no preference for either half of the mat. 
A piece of linen quartered black and white (Fig. 1 B) was next used to 
cover 39 lice exposed to the sun. After 10 minutes, 30 lice were found beneath 
the white, 7 beneath the black, and 2 were found crawling upon the black. 
The thermometers registered 38-5° and 31° C. respectively beneath the black 
and white. In this case, therefore, when exposed to 38-5° C. beneath black, 
the insects preferred to face the bright light beneath the undyed linen than 
the higher temperature beneath the blackened portion. 
The foregoing experiments demonstrate that black clothing repels lice by 
virtue of its capacity for absorbing radiant heat. 
Conclusions. 
Man's clothing, depending upon its colour, varies in its capacity for 
absorbing radiant heat. In warm weather, black cloth, which absorbs the 
maximum of heat rays, will prove inimical to lice and cause them to wander 
away to where it is cooler so as to escape (n) the direct effect of heat, and 
( b) its indirect effect in producing perspiration in man, for lice object to ex¬ 
cessive moisture in vicinity to man. 
3. THE INFLUENCE OF BLACK, WHITE, AND COLOURED BACKGROUNDS 
AND OF COLOURED SCREENS UPON PIGMENTATION IN LICE, PROVING 
THAT PIGMENTATION IS NOT HEREDITARILY TRANSMITTED. 
(a) DEGREES OF PIGMENTATION OBSERVED IN LICE OBTAINED FROM 
VARIOUS RACES OF MAN. 
Murray (1861, p. 571) states that the colour of lice found on different races 
of man varies, being “nearly black'’ on West Africans and Australians, dark 
and dusky on Hindus, orange on Mozambique Africanders and Hottentots, 
yellowish brown on Chinese and Japanese, dark brown on Andes Indians, 
dusky olive on Californian Indians, whilst on Esquimaux the lice are paler and 
more approaching those found on Europeans. He illustrates the tarsi and 
antennae of specimens obtained from the various races named. 
Darwin (1880, p. 169), refers to Murray's paper, and writes that lice from 
Sandwich Islanders “were darker coloured and appeared different from those 
proper to the natives of Chiloe, in South America." 
As Murray (Ibid. pp. 567-571) pointed out, the general colour of lice is due 
to (a) their integumentary pigment, and ( b ) the colour of their gut contents. 
