A. Bacot 
229 
humanus, is probably due, at all events in part, to the method of feeding 
and other conditions of captivity. 
Origin of the strains experimented with. 
Lice were obtained from three separate sources; a London Borough 
Infirmary, one of the London County Council cleansing stations, and 
a Salvation Army shelter. I take this opportunity of recording my 
thanks to the Officials of these Institutions who so kindly assisted me 
by providing material. 
The insects obtained from these sources were placed together and 
treated as a single stock in the case of P. humanus. With P. capitis, 
however, two stocks were kept; one raised from nits on the hair and 
the other from active insects received with the hair. This course was 
pursued in order to avoid possible error due to a mixed infection, but 
as no difference in size, structure, or habits was observed between the 
two stocks, it was concluded, after several generations had been bred, 
that only P. capitis had been present. Subsequently either stock was 
drawn upon to supply insects for experiment. 
Methods. The method of breeding employed was essentially the 
same as that adopted by the author when experimenting with fleas 
(Bacot 1914), in one particular adaptation to the circumstances it 
closely paralleled a feature of the method mentioned by Sikora (1915), 
the idea, however, was differently applied. 
The insects were kept in glass-bottomed entomological boxes lined 
with a loose slip of cloth to give foothold. In the case of P. capitis 
a small tuft of hair was also generally added, although it was found 
not to be essential. The open top of the box was covered with chiffon, 
the lid being partly closed over it to keep it stretched while it was 
securely tied in position with fine thread; as an extra precaution 
against escape the box was nested in one of a larger size. Feeding 
took’ place readily through the chiffon when this was placed against 
a suitable skin surface. As it was necessary during the progress of the 
research to feed isolated individuals or families in as many as three 
dozen separate boxes at once, small ones of three quarters of an inch 
diameter were used. Holes punched in pieces of card into which the 
gauze covered boxes were inserted, enabled them to be kept in position 
against the body during sleep, with the aid of a flannel belt. The insects 
had the option of feeding at any time covering a period of six or seven 
hours during which the chiffon covered openings of the boxes were 
against the skin. 
