G. H. F. Nuttall 
489 
Bacot (MS. Report, W.O. 20. hi. and 13. iv. 1917) liberated lice 
upon a sheet of paper placed on a table in front of a window; a strip of 
paper 7-10 mm. broad, smeared with the repellant to be tested, was 
placed athwart the path pursued by the lice in walking away from the 
source of light. It will be seen that some substances gave negative and 
others positive results: 
iSxpt. 
No. Substance tested 
1 Oxford grease 
2 Vermijelli 
3 Naphthaline 25 % and Ox¬ 
ford grease 75 % 
4 Crude “Parasitox” 
5 Naphthaline, crude, 90 % 
and soft soap 10 % 
6 Carbolic acid, crude, 5 % 
and soft soap 
7 Crude naphthaline 47-J %, 
carbolic acid 2i%, Ox¬ 
ford grease 50 % 
8 Naphthaline, crude, 25%, 
carbolic acid 2J%, Ox¬ 
ford grease 72 % 
9 Naphthaline, crude, 25%, 
Oxford grease 75 % 
Negative evidence as to repellants may be considered under four 
headings: 
(1) It has been found that persons may be attacked under natural 
conditions in spite of applying so-called repellants to their persons. 
This oft-repeated experience led some authors to condemn repellants 
as useless in practice. It is difficult to check the value of such evidence. 
(2) So-called repellants placed on persons or their clothing, or 
tested in vitro, do not repel lice under experimental conditions. Thus 
Nocht and Halberkann (1915, p. 626) observed no repellant effect from 
“various reagents.” Wulker (1915, p. 628) found that lice ran toward 
substances which should have repelled them. Heymann (vm. 1915, 
pp. 311-312) saw no evidence of naphthaline, “ Globol” and “Lausofan” 
exerting a repellant effect either in vitro or when smeared upon the 
skin. Frickhinger (1916, p. 1254) smeared various essentia! oils, insect 
powder, naphthaline, etc. across their path or upon the shaved skin of 
a guinea-pig, and found that the insects were not repelled thereby. 
Result 
Of 20 lice all crossed barrier unhesitatingly 
99 99 99 99 99 
Of 20 lice 4-5 crossed barrier, 2 turned back thrice, 
and 14 walked along barrier to end 
Of 21 lice 16 crossed barrier eventually whilst 5 
turned back after 2-3 attempts. There was more 
hesitation than in experiment 3 
Of 20 lice 17 crossed barrier, with less hesitation than 
in experiment 4 
Of 20 lice 11 crossed barrier eventually and 9 turned 
back. They were baulked by the barrier at a 
distance of 4—5 mm. 
Crossed barrier 
unhesitatingly Hesitatingly Repelled 
3 9 5 
6 5 C 
9 3 
