336 
high degree of toxicity to lice, and the 
toxic action persisted for an unusually 
long time. 
Tests were made with various con- 
centrations of the product, using many 
types of preparations. A 10-percent 
DDT powder was shown to kill all lice 
on an infested subject and provide pro- 
tection against reinfestation for at least 
3 weeks. This was the type of mate- 
rial we were looking for. Our chief 
worry was: Can the chemical be used 
safely on man? The Food and Drug 
Administration was attempting to de- 
termine the answer to this question. 
After several months of intensive study 
they concluded that in dust form DDT 
was entirely safe to use. By May 1943 
DDT was recommended to the armed 
services as a safe and effective louse 
powder. 
The success of DDT in controlling 
lice and typhus, as demonstrated by 
scientists in the North African War 
Theater, the U. S. A. Typhus Com- 
mission and the Rockefeller Founda- 
tion, is a story in itself that should be 
told by those agencies mentioned. It 
will suffice to say that we had more 
than gained our major objective. We 
now believe that DDT provides the 
means of not only controlling lice and 
typhus but of eventually eradicating 
typhus from the earth. 
Other developments—The work on 
louse powders represented the most 
important developments in connection 
with the louse program. However, 
many other significant contributions 
were made and the two most outstand- 
ing are listed below: 
1. It was found that DDT was far 
more effective and persistent when 
impregnated in clothing than when 
employed as powders. When impreg- 
nated in the underwear at suitable 
concentrations the DDT continues to 
1 Swiss workers, as we learned after our 
studies were well advanced, had demon- 
strated the value of DDT as a louse insecti- 
cide, and the Geigy firm was producing a 
product for this purpose called Neocid which 
contained 5 percent DDT. 
ANNUAL REPORT SMITHSONIAN INSTITUTION, 1948 
kill body lice for as long as 6 months 
provided the clothing is not washed. 
If laundered according to usual pro- 
cedures, the clothing remains effective 
even after 4 to 8 washes. 
2. A liquid preparation known as 
the NBIN formula was developed for 
the control of lice, especially head lice. 
This was prepared as a concentrate 
which when diluted with 5 parts of 
water contained approximately 1 per- 
cent of DDT, 2 percent of ethyl p- 
amino benzoate (benzocaine), 11 per- 
cent of benzyl benzoate and 2 percent 
of an emulsifier known as a poly 
oxyethylene derivative of sorbitan 
monooleate. 
Mosquitoes 
More attention was given to various 
aspects of research on mosquito con- 
trol than to any other project. This 
was justifiable because mosquitoes as 
a group are probably the most im- 
portant insects in the field of medical 
entomology. Investigations on this 
problem concentrated along three 
major lines of research: (1) larvicides, 
(2) insecticides for adult mosquitoes, 
and (3) repellents. 
There are hundreds of species of 
mosquitoes, which vary in their habits 
and resistance to insecticides and 
repellents. It was possible to carry 
out extensive studies on only a few 
representative species. For the labor- 
atory aspects of the program two 
species were chosen, the malaria mos- 
quito (Anopheles quadrimaculatus) and 
the yellow fever mosquito (Aedes 
aegypti). The rearing of large numbers 
of mosquitoes which were needed for 
research on larvicides, adult sprays, 
and repellents, was a major under- 
taking in connection with the research 
project. The Anopheles are not easily 
reared under laboratory conditions in 
large numbers, but as many as 50,000 
mature larvae or adults were needed 
each day during the peak of the pro- 
gram. Plate 2, figure 1, shows one 
of the rearing rooms for the Anopheles 
colony. 
