108 
Biology of Pediculus humanus 
was fixed to it by gum arabic, and, after t his had dried, the whole 
of the chiffon with its silk thread, as well as the top chiffon, were im¬ 
pregnated with shellac varnish, the object being to cement the fibres 
of the chiffon to each other at their points of crossing, thus strengthening 
the grating and ensuring against the escape of small lice through the 
apertures of the fabric whose fibres may otherwise become displaced. 
Fig. 2 E illustrates the size of the grating in the shellacked chiffon 
in relation to an unfed first stage larva, showing that the apertures 
are too small to permit of the escape of the louse whilst not obstructing 
its movement when it desires to feed. Upon the floor of the pill-box 
was laid a small snugly fitting frame of fine soft steel wire about 0-5 mm. 
thick, the frame being wound round with a long hair (as shown in Fig. 2 
D) knotted to the frame at both ends, and firmly fixed to the crossings 
with the wire by means of shellac applied with a feather. The frames 
were removed and replaced by others every day or two according as 
they became charged with eggs. The different frames in a series were 
distinguished by small coloured glass beads strung on the wire, and 
the eggs laid on each day were spotted by means of a fine camels’ 
hair brush with different coloured inks, thus permitting accurate 
registration of when they were laid. The rest of the apparatus will be 
readily understood by reference to Fig. 2, and the descriptive legend 
accompanying it. The lower part of the box is first placed in the 
round hole in the wrist strap (A), the lice are put in the box, the top 
chiffon is then placed in position and the lid closed down upon it; the 
strap is then applied to the arm as shown at (B). The strap is of the 
ordinary form used for sprained wrists. The looping of the strap upon 
itself holds the lid of the box down firmly in jfiace, and the bottom 
chiffon is pressed down upon the skin, the pressure being regulated 
by suitably tightening the strap. 
Both my Laboratory Assistant, Mr C. Harpley, and myself wore 
the strap on the wrist day and night for weeks whilst raising broods. 
The box was shifted periodically from one wrist to the other, up the 
arm, or from the front to the back of the arm. After three weeks 
the biting of a hundred lice repeatedly upon the same spot produced 
increasing irritation and I transferred the strap to the knee, wearing 
it like a garter. The temperature between the box and skin varied 
but slightly day and night (32-34° C.). That the box shifted little was 
shown by the impress it left upon the skin and the corresponding 
circular pattern made by the bites inflicted by the lice. The method 
here described will be referred to as the wristlet method in subsequent 
