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THE BIOLOGY OF PEDICULUS HUM ANUS. 
SUPPLEMENTARY NOTES. 
(1) Colour and Light Reactions. (2) The influence on lice of temperature condi¬ 
tions in clothing and the absorption of radiant heat by cloth. (3) The influence 
of black, white, and coloured backgrounds and of coloured screens upon pigmen¬ 
tation in lice, proving that pigmentation is not hereditarily transmitted. (4) The 
relative proportions of the sexes. 
By GEORGE H. E. NUTTALL, E.R.S. 
(From the Quick Laboratory, University of Cambridge.) 
(With Plate X and 1 Text-figure.) 
1. COLOUR AND LIGHT REACTIONS. 
Only one author has hitherto touched upon the subject of the reactions of 
lice towards colour, namely, Galli-Valerio (xii. 1916, p. 35), who, learning 
from a Serbian doctor that black clothing is stated to repel lice, carried out 
one experiment wherein he placed the insects upon variously coloured paper 
and counted the number that wandered to each colour. The results recorded 
permit of no conclusions, no particulars are given regarding the manner in 
which the experiment was performed, and consequently it remains to be 
determined if lice react to colour. 
Sources of experimental error. 
In Parasitology , x. pp. 176, 100, reference was made to certain reactions to 
light that are exhibited by P. humanus and how they wander away from a 
source of light toward the shade. Indeed, I have found that they are so 
sensitive to different intensities of illumination that if light from a window 
falls upon them from one side, whilst it is reflected in upon them from the 
opposite direction by a mirror, the insects wander away quickly from the 
window side to the mirror side of the experimental cell in which they are 
confined although the difference in the intensity of the illumination from the 
two sides is but slightly appreciable to the human eye. It is therefore essential 
in testing the preference of lice for white, black or coloured backgrounds that 
the insects should be exposed to vertical illumination. Slightly oblique rays 
will invariably cause them to wander to one side; this being conveniently 
observed by placing the cell upon a stool with a top that is rotated periodically. 
Since experiments conducted with single or but few insects would consume 
much time, it is best to use many lice, but their tendency to collect in a mass 
