274 
Hot Air Disinfestor 
4. It has not been demonstrated that any article of clothing is in any 
way damaged by this process. 
For practical purposes, the material for disinfestation should be exposed 
to a temperature as recorded by the wall thermometer, of 75° C., or higher 
for twenty minutes. Since the louse and the nit are killed at 50° C. and 
55° C. respectively (Nuttall), this leaves a considerable margin of safety. 
Through the kindness of the Director General Medical Services B.E.F., 
I am permitted to publish the results of an independent investigation under¬ 
taken by Captain T. J. Murray, M.Sc., Ph.D., R.A.M.C., T.F., working under 
the direction of Colonel W. W. 0. Beveridge, C.B., D.S.O., A.D.M.S. Sanitation, 
B.E.F., with a view to observing the working of this disinfestor and more 
especially in order to measure the temperature reached in the clothing during 
the process of disinfestation. 
The apparatus employed for the measurement of the temperatures was 
brought to France especially for this purpose by Colonel Beveridge, and 
was formerly used by him in the measurement of temperatures reached in 
the interior of foods during the process of cooking. It consists of an electro 
thermo-couple, with a milli-voltmeter in circuit. The electro thermo-couple 
is made of two long pieces of wire of different metals soldered together at 
their ends, and insulated throughout their length. One wire consists of copper 
and the other of an alloy known as constantan. In such a circuit, if one junc¬ 
tion is at a higher temperature than the other, a current of electricity is 
generated in the wire. The greater the difference in temperature at the 
junctions, the stronger is the current in the wire. The milli-voltmeter indicates 
the strength of the electric current set up in the wire circuit. 
If one junction is kept at a constant low temperature, by placing it in 
melting ice at 0° C. the current strength varies with the temperature of the 
hot junction. 
In these experiments, the milli-voltmeter and the cold junction were 
placed outside the chamber, the insulated wires were passed through an 
opening into the disinfestor, and there was sufficient length of wire to allow 
of the other junction being placed at any point of the clothing, in any region 
of the chamber. 
By simply noting the readings on the milli-voltmeter, the temperature 
at the point of the clothing occupied by the hot junction can be registered. 
The process is continuous, and all variations in temperature can be observed. 
Captain Murray reports: 
“ Eleven completed chambers were examined and of these two had 
faults of construction which would have rendered them inefficient. In one 
of the faulty disinfestors, the braziers were made half-size, and would thus 
be incapable of maintaining the requisite supply of hot air. In the other, 
the walls were badly packed and the truck-rails entered the chamber at an 
angle, so that the clothing rested against one wall, and left a free space of 
