Gr. H. F. Nuttall 
431 
The authors quoted do not state how they conducted their experi¬ 
ments or whether lice exposed for shorter periods survived. Some obser¬ 
vations by Heymann and Zucker are omitted from the table because 
they relate to needlessly long exposures. Prowazek (1915, p. 67) makes 
the absurd statement that lice die at 35° C. Bacot and Widmann are 
the only authors who mention the stages with which they experimented. 
Except in one case my experiments were carried out with adults 
aged 5 weeks that had gorged 15-20 minutes prior to the test. The lice 
were dropped into small glass dishes resting on a cardboard box in a 
microscope-thermostat. A thermometer bulb rested on the floor of one 
of the dishes. The behaviour of the lice could be watched through the 
thermostat window, and the dishes, when exposure time was up, were 
quickly removed by forceps through the small hand-hole at the side 
without affecting the temperature inside. Exposed to heat, the lice at 
once became greatly agitated, in most cases voided excreta after a few 
seconds, and soon rolled over on their backs, their movements gradually 
subsiding. Some survived in an almost immobilized condition, others 
recovered completely and were as lively as ever after 24 hours (at 30° C.) 
provided they had not been exposed too long to the heat (vide table). 
We may therefore conclude that adult lice are killed by dry heat 
at 65-70° C. in 1 minute, and at 55° C. in 5 minutes. 
(c) Degree of Heat recommended in practice. 
Killing of nits and 
active stages on clothes. 
In the following 
table I have summarized the 
statements found in 
the literature: 
Temperature 
'C. 
(dry heat) 
Time of 
exposure 
in minutes 
Result 
+ =killed 
Authority (reference 
see p. 435) 
120-130° 
20' 
+ lice roasted, nits crisp and crackly 
Seligmann and Sokolow- 
sky (apparatus, see 
p. 439) 
100-110° 
30' 
+ ditto . 
9J 
o 
O 
co 
60' 
+ . 
Heymann 
60° 
60' 
+ (on furs and leather) . 
Uhlenkuth 
50-58° 
15-25' 
+ . 
Engelhardt 
It is evident that the foregoing authors, Engelhardt excepted, em¬ 
ployed needlessly high temperature or unnecessarily long exposures for 
the purpose of killing lice; the experiments previously cited prove this 
conclusively. It seems absurd to waste fuel and time when the same 
