G. H. F. Nuttall 
429 
results, i.e. those in which they found that lice or nits survived exposure 
to certain insecticides. 
The relative resistance of the various stages of Pediculus humanus. 
Most authors have failed to note any difference in the resisting power 
of lice at various active stages of their development. Prowazek (i. 1915, 
pp. 67-68) asserts that adults are more readily killed than larvae, whilst 
Legroux (vm. 1915, p. 470) states that old females and young lice are 
the most susceptible; these statements are contradictory. According to 
Busson (1915, p. 674) freshly gorged lice are more susceptible than 
others to the effects of insecticides. In any case, such differences are 
not of importance; in practice the nits have to be destroyed and any 
method that falls short of killing them is bound to be ineffective. 
The experimental evidence points to nits and active stages being 
about equally susceptible to the effects of heat whereas, as might be 
foreseen, nits are the more resistant to the influence of insecticides. 
This is rendered most evident by the experiments with vapours. It 
follows that the value of insecticides should be determined on nits and 
not on the active stages unless merely temporary results are to be ob¬ 
tained, treatment being repeated periodically. 
I. DESTRUCTION OF LICE BY HEAT. 
Experimental Section. 
Regarding the temperature that is required to kill corporis. 
1. Dry Heat. 
(a) Experiments with Nits. 
Temperature 
•c. 
Length of 
Result 
Authority 
exposure 
+=killed 
(reference 
(dry heat) 
in minutes 
o survived 
see p. 435) 
72° 
1/ 
+ 52 nits 4 days old at 30° C. tested. All slightly 
clouded, many shrunk. All killed, Its of con¬ 
trols hatched ... 
Nuttall 
70° 
].' 
+ 
and shrivelled 
11 
70° 
5' 
+ 
... ... ... ... ... ... ... 
Friedmann 
65° 
1' 
+ 
mostly shrivelled 
Nuttall 
62° 
5' 
+ 
shrivelled 
11 
61° 
10' 
+ 
>5 * * * * * * 
19 
60° 
5' 
+ 
and dried at once (3 nits) 
Widmann 
60° 
20' 
+ 
Lelean 
55° 
10' 
+ 
and shrivelled (3 nits) 
Widmann 
54° 
35' 
+ 
Bacot 
52° 
30' 
+ 
and 50 % shrivelled ... 
Nuttall 
50° 
15' 
+ 
and shrivelled 
Widmann 
49° 
25' 
+ 
but not shrivelled 
Nuttall 
45° 
15' 
O 
2 nits survived exposure 
Widmann 
28—2 
