180 
Biology of Pediculus humanus 
DO LICE POSSESS AN OLFACTORY SENSE? 
The evidence so far collected is all negative. Peacock (1916, pp. 
42-44) found that corporis were not attracted to recently discarded 
sweat-impregnated clothes. Frickhinger (1916, pp. 1254-1256) has 
published a long-winded account of experiments which prove nothing, 
but from “field experience” he concludes that lice do smell certain 
persons (!). A series of experiments made by me with different essential 
oils and other substances commonly described as repellants, show that 
either in dilute or concentrated form they do not repel hungry lice; 
the insects feed upon man in spite of so-called repellants; the latter 
are really insecticides, and, as such, will be considered in a later section. 
According to Hase (xi. 1915, p. 158) some contend that persons having 
to do with horses are not attacked by lice, but he has not found this 
to be true 1 . Neither has Hase found that freely perspiring men, and, 
incidentally, hairy men, are more often attacked than others. 
GREGARIOUSNESS. 
Lice show a marked tendency to congregate in masses ; this is observ¬ 
able in all stages. According to Racot (it. 1917, p. 232) the tendency 
is less marked in the larvae of capitis than of corporis, but I have been 
unable to detect any difference. 
Vital Resistance 
TO IMMERSION IN WATER, COLD, EXPOSURE TO A VACUUM, AND TO 
MECHANICAL PRESSURE. 
Immersion in water. Lice are able to resist immersion in water for 
a considerable time. The authors who have tested this resistance, do 
not state how they performed their experiments or with, what stages 
they operated; we must presume that some of the insects were adults. 
Muller (1915, p. 54) saw lice revive after 22 hours’ immersion; he 
cites Pick (1915) as having observed sham death in lice that had been 
submerged. Kinloch (1915, p. 1038) found that lice survived immersion 
in water for 48 hours, and in normal salt solution for 60 hours; he 
records neither the number of lice tested nor the temperature. Hase 
1 It is stated by Railliet (1895, p. 803) th&t fleas are repelled by the odour of horses; 
possibly the two insects have been confounded in this regard. 
