Gf. H. F. Nuttall 
179 
the temperature being too high, though the tube was not unpleasantly 
hot to the hand. This explains a very interesting observation made by 
Howlett, of which he told me, namely that an ordinary comb, when 
warmed and passed through caphhs-infested hair, causes the insects to 
become very active, they swarm out from near the scalp and are readily 
combed out. He recommended the method, for practical trial, to his 
Indian assistants, and they subsequently reported that their female 
acquaintances were delighted with the practical results they obtained 
by this simple means 1 . 
Effects of warmth on activities and metabolism. 
Activities. The effect of temperature on the activities of lice is 
very marked. At 0° C. they are immobilized, at 10° C. they move 
very slowly, at 20° C. they are fairly active, at 30° C. they are very 
active, and at 37-40° C. they are extraordinarily active creatures; 
all grades of activity are observable at intermediate temperatures. 
If the temperature is raised above 40° C. they become wildly active and 
soon succumb to exhaustion. They die in a few minutes at 45-50° C. 
The climbing records of lice on hair (see p. 101) demonstrate that 
capitis is more active than corporis at 17-18° C., and that corporis may 
climb more than twice as fast at 30° C., than it does at 17-18° C. As 
stated elsewhere, lice have been observed to abandon persons in high 
fever, and to wander actively from individuals when these are lying 
close together and warm. 
Metabolism. Development and digestion are arrested at low 
temperatures, thus whilst hatching occurs in 16 days at 25° C., it takes 
place in 4-7 days at 37° C.; oviposition does not apparently take place at 
below 20° C., and 37° C. or slightly over is about the upper limit. 37° C. 
appears already to be too high, for in thermostat experiments, only 
54-3 % of the larvae hatched out at that temperature, whereas 70-80 % 
hatched out at 30° C. Digestion, as gauged by lice that have gorged 
themselves, does not take place at 12° C., even if the insects survive 
4-5 days, whereas at 35-37° C. it is complete in about 5 hours. Lice 
can be raised at 28-37° C., but the best results are obtained between 
30 and 32° C. 
1 See p. 186. 
