450 
Combating Lousiness 
Remarks. 
In the foregoing methods of hot-air disinfestation there are two 
practical difficulties to be met: (1) the unequal distribution of the heat 
in the chamber, this being most marked in large and high chambers, the 
temperature below being much lower than above. The contrast in tem¬ 
perature will necessarily be greater in flimsy structures in exposed 
situations especially in cold weather. In the hut (Model A) used by Grant 
the floor and ceiling, temperatures in two instances recorded were (a) 37° 
and 103° C. and ( b ) 68° and 120° C. respectively; therefore in practice 
the minimum lethal temperature should be registered in the lower part 
of the chamber. The difficulty can also be overcome by only exposing 
articles in the upper half of the hut as already suggested on p. 443 or 
by mixing the air in the chamber by means of fans driven by hand or 
otherwise. Judging from the plans alone, in the absence of recorded 
thermometric readings, the stratification of the air in the chamber ac¬ 
cording to temperature (hot above and cold below) should be less marked 
in Model C than in Models A and B, whereas in Model D, judging merely 
from the description, the temperature should be fairly uniform throughout 
the space, this being a most desirable feature. (2) If moist articles are 
placed in a hot-air chamber, they will be kept cool as long as evapora¬ 
tion continues, therefore they should be kept in the chamber sufficiently 
long (a) to become dry and ( b ) to be disinfested. In practice, dry articles 
are maintained at 65° C. (thermometer 4 inches from the floor) for 30 
minutes, whilst damp articles are exposed for 60 minutes. 
Captain Orr (22. iv. 1918) writes that it is impossible in damp weather 
to get rid of all the moisture in the chamber. He has sent me scale 
drawings of two new designs of huts which, while burning any fuel, are 
planned, most ingeniously, to ensure the adequate circulation of hot dry 
air in the chamber. 
Incidentally, I desire to put on record that the credit for having first 
employed hot-air huts belongs entirely to Captain Orr, who erected and 
proved the efficiency of one built at Shorncliffe in the end of. 1915. 
The tests subsequently carried out by Grant and Peacock were conducted 
with this identical hut. 
Regular Apparatus. 
Although not primarily intended for the purpose, all large jacketed 
steam disinfectors can be used as hot-air disinfestors if required (see 
footnote, p. 469). This is accomplished by admitting steam into the jacket 
only and allowing heated air to enter and circulate in the chamber as is 
