100 
Biology of Pediculus humanus 
A few experiments, carried out by me in sunlight, show that the 
locomoto'ry powers of lice have been greatly underestimated, judging 
from the records above cited. ■ Thus two corporis females (Lot 212) that 
had gorged three hours previously and had been maintained at 30° C., 
were placed upon a large piece of cloth on a window bench upon which 
the sun shone. The air temperature registered 18° C. in the shade, and 
a thermometer placed beneath the fabric rose to 24-5° C. The insects 
walked very rapidly over a distance of 30 cm., as follows, as timed in 
minutes and seconds by a stop-watch: 
Female 
Time 
Material traversed 
Direction 
a 
1' 37" 
black sateen 
horizontal 
a 
49" 
' „ ,, 
99 
b 
V 40" 
99 99 
99 
b 
V 41" 
99 99 
99 
b 
2' 53" 
99 99 
angle of 45° 
b 
2' 53" 
99 99 
99 99 
a 
2' 51" 
rough cloth 
horizontal 
a 
2' 10" 
/9 99 
These records show that ? a, in her second run, actually travelled 
at the rate of 1 metre in 2' 43" on black sateen. The rate of locomotion 
in $ b went like that of a clockwork in four successive runs, only a 
difference of 1" occurring in two horizontal runs, whilst the two runs 
at 45° agreed exactly in point of time (2' 53"). The records show clearly 
that it takes lice longer to ascend at an angle of 45° than to traverse 
a horizontal surface, i.e. about as long as to traverse rough cloth 
horizontally. 
( b) On Hair. 
As‘it seemed to me of interest to determine the speed with which 
pediculi may climb along human hair, I constructed a simple, apparatus 
for the purpose. This consisted of an oblong bent glass frame to which 
a ruler with centimetre scale was attached by crossed rubber bands; 
two long human hairs were stretched between the bands, and the frame 
was clamped to a stand which held it in any position desired. The 
two hairs were ca. 1 mm. apart and parallel, but they could be readily 
separated still furthec by an intervening object. When gently handled 
with fine forceps, the head being pointed in the desired direction, the 
insects promptly climbed along the hairs behind which the scale could 
be read. The timing was done with a stop-watch. 
When climbing two hairs, the louse uses all its legs, grasping both 
hairs with the legs of each side, whereas in climbing a single hair, capitis 
