G. H. F. Nuttall 
389 
may be innocently acquired; the infants, or a whole family of small 
children may become infested through a verminous mother, father, or 
other adult, or the parasite may be transmitted from child to child. 
Similarly, when persons live in close contact with one another, as soldiers 
do in barracks or billets, there is no question again but that, infestation 
may arise innocently. 
A certain number of insects become scattered through the frequent 
scratching that accompanies infestation, so it is possible for an individual 
to become infested through contact with clothing, bedding, the seat of 
the W.C., and possibly public vehicles and benches, and there is no 
doubt but that this occurs more often than is generally supposed. Apart 
from direct personal contact then, the parasite may be spread indirectly. 
In the course of my experiments, I several times observed the 
shedding of single hairs bearing freshlg laid eggs, and it therefore appears 
to me that this probably constitutes the more frequent mode of dis¬ 
semination, although it has hitherto been completely overlooked. Any 
adult person can convince himself readily that pubic and body hair is 
shed under ordinary circumstances, by examining the floor of the tub 
in which he has bathed and from which the water has drained away. 
These hairs are continually being shed upon the underclothes, and they 
are more plentifully shed in the act of coitus or through scratching. It 
therefore needs little imagination to understand how the parasite can 
be conveyed either directly from person to person, or indirectly by 
means of shed nit-bearing hairs which may become entangled in the 
pubic or other hair of a clean individual. 
Whereas the nit, and usually the first stage larva during the first 
day or two after hatching, is found attached to a single hair, the active 
stages cling as a rule to the bases of two hairs, therefore it is less likely 
that the older lice wfill become detached when the hair is shed, although 
it is of course possible that older larvae and adults may occasionally be 
set free. 
Again, owing to its much greater structural adaptation to a parasitic 
life than is the case in P. humanus, the crab-louse is a very helpless 
creature when it is removed from the hair to which it normally clings. 
If placed upon cloth or any surface devoid of hair, it can make practi¬ 
cally no progress. If a hair is brought near it r;nder such circumstances 
it at once grasps it firmly. Under natural conditions it clings continuously 
to hair, shifting from hair to hair when disturbed, without relaxing its 
hold upon one hair before seizing the next. To detach the crab-louse 
without injury, it is necessary to slide it along the hair from base to 
