It is important that the disinfestor be built according to plan, attention 
being paid to: 
(а) Selection of site in relation to bath house; 
(б) The packing of the walls with clay; 
(c) The arrangements of the openings in floor; 
(d) The position of the switch or turntable. Its distance from the door 
of the chamber must be at least half the length of the rack plus 
half the wheel-base of the truck; 
(e) The location of the air inlet and air outlet pipes; 
(/) To prevent warping, the framework of the truck should be made 
of heavy wood. Iron should be used if possible; 
(g) The door of the entrance to the pit, and the two pairs of doors 
to the chamber, must be tight fitting. 
The difficulties met with in employing hot air as a means of disinfestation 
are due to the fact that the specific heat of air is very low, and on account 
of that a constantly moving supply of freshly heated air is necessary in order 
to raise solid articles quickly to a temperature that is lethal to vermin. 
In this disinfestor, the hot air and gases from the coke braziers in the 
pit are distributed by the perforated iron floor, and then sweep upwards 
through the disinfesting chamber, and ultimately escape through the series 
of vent pipes distributed along the top of the walls. Thus, there is a regular 
and rapid change of hot air at the surface of clothing suspended in the chamber. 
The total sectional area of the vent pipes is greater than that of the cold 
air inlet pipes in the ratio of three to two. This ratio is somewhat greater 
than is necessary to allow for the increase in volume of the air on being 
heated and on being enriched with gases from the burning coke. No resistance, 
then, is offered to the escape of the slightly expanded air. 
' I have made daily temperature observations during the working of a 
large number of these disinfestors. In some of them the observations covered 
a period of two months. The measurements were taken with ordinary chemical 
thermometers placed in various parts of the chamber, and with naphthalene 
tubes melting at known temperatures. In the majority of tests, lice and 
nits were placed in the clothing with the thermometers. 
The results may be summarized as follows: 
1. In fair weather, when the clothing is dry, a temperature (55° C.) 
sufficient to kill lice and nits in ten minutes is invariably attained 
beneath the folds of the clothing in from one to five minutes. 
2. In stormy weather when the clothing is wet and cold, this lethal 
temperature is invariably attained in from five to fifteen minutes. 
3. The temperature beneath the folds of the clothing lags from ten to 
fifteen degrees centigrade below that of the surrounding air, as 
registered by the right angle elbow thermometer built in the wall 
of the disinfestor. 
