Gr. H. F. Nuttall 
161 
fertile eggs, the only two failures being due to an arrested development 
in the egg, and to a death in the second larval stage. A second trial 
with 104 fertile eggs yielded 103 larvae; five larvae died without feeding, 
and there was but one case of arrested development. A third trial, with 
a batch of 507 fertile eggs, gave 4 cases of arrested development whilst 
4 larvae failed to free themselves from the egg-shell in hatching, con¬ 
sequently, at this stage, the loss of life was less than 2 %. In a fourth 
experiment, carried out during warmer weather, the result was not so 
favourable; thus of 247 fertile eggs, 3 showed arrested larval develop¬ 
ment and no less than 64 larvae died in the act of emerging, the loss of 
life therefore amounted to about 27 %. This observation is of interest 
as showing that in summer during hot weather there may be an in¬ 
creased loss of life in lice upon the human body, and it bears out what 
has been stated on p. 87 regarding the seasonal incidence of lice. 
The Duration of the Life-cycle of P. hum an us when maintained 
CONTINUOUSLY UPON THE HUMAN BODY. 
(a) Corporis. 
The following experiment was carried out by the felt cell method 
(see p. 105), the insects being kept continuously on the arm and having 
direct access to the skin, as in nature. 
On 2. ii. 16, 5 dd and 5 $?, received that morning from Dr W. H. 
Hamer in London, were placed upon the arm after being fed. On the 
afternoon of the following day (Day 1 of the protocol) the lice were 
removed, 25 eggs having been laid in the cell. Of these eggs 22 were 
fertile, all hatching normally at a subsequent date. The arm was 
inspected daily at 10-11 a.m. and the following results recorded: 
Day 
3. in 16 1 
8 
10 
11 
12 
13 
14 
15 
16 
22 fertile eggs laid on the felt 
16 eggs had hatched, 16 1st stage larvae counted 
6 remaining eggs had hatched, 4 1st stage and 18 2nd stage larvae counted 
4 more 2nd stage larvae found, making total 22 
13 2nd stage larvae and 9 3 rd stage larvae found 
4 2nd stage larvae and 18 3rd stage larvae found 
22 3rd stage larvae found 
10 3rd stage larvae and 12 adults (2 £ and 10 $) found. All but 2 £ and 
2 $ were now removed, copulation occurred, a.nd the females ovi¬ 
posited as detailed on p. 129. 
first eggs laid 
The time required to complete the life-cycle, from egg to egg, was 
therefore 16 days, made up as follows: Developmental period in the 
Parasitology x 11 
