486 
Combating Lousiness 
containing them may be used alone or in combination with heat, and 
mechanical methods of removal. They may be applied in a variety of 
ways, either alone or with other ingredients in the form of powder, 
solution, emulsion, suspension in fluid or ointment, as a vapour or gas. 
An insecticidal fluid may be used as a wash, dip or spray, and, like 
powders, may be confined to sachets whence the toxic vapour escapes 
into the atmosphere between the clothing and body. In some cases the 
insecticide should be dispelled before the clothing is worn, in others not, 
this depending upon the degree of toxicity it possesses for man. 
Powders. Numerous powders charged with insecticides have been 
extensively used and recommended. There are several objections to 
powders: (1) they are a wasteful method of applying the insecticide, 
(2) the latter is very unevenly distributed upon the clothing and indi¬ 
vidual and a great deal too much of it may come in contact with the 
skin, (3) a powder always tends to gravitate and may accumulate where 
it is not wanted, (4) the vehicle with which it is mixed may be unsuited 
for coming in contact with perspiration, (5) a powder, especially when 
it contains chalk or starch., may soil the clothing. 
Sachets have a very limited radius of action and it is doubtful if they 
give results at all commensurate with the labour and cost they involve. 
Sprays necessarily offer an imperfect means of applying insecticides 
to man and his clothing, but there are circumstances in which they may 
be useful. 
Impregnated clothing. The ideal method of using insecticides upon 
the person should consist in the impregnation of the clothing therewith; 
for this purpose the insecticides should not be injurious to the skin, 
not soil the clothing, not be too volatile, and be removable by washing. 
This ideal, however, remains to be attained (see p. 500). 
The Effects of Greasy Substances and Oil. 
In the section on the biology of Pediculus humanus reference was 
made (p. 85) to the remarkable immunity to head-lice observed in 
certain classes of negroes in the United States, this immunity being 
attributed to the liberal use of pomades and cosmetics upon the hair 
of the head. Fiebiger (vn. 1915, p. 645) states that greasy-headed 
people are free from capitis, and Nysten (1858, p. 1140) and Perroncito 
(1901, p. 597) mention olive oil as a cure for head-lice; the former refers 
to it as an infallible and simple remedy. Brumpt (1910, p. 550) records 
from his travels that melted butter is applied to the head by the Somalis, 
