44 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
A rat, heavily infested with lice, was isolated and dusted as 
previously mentioned with five pinches of powder No. 2 (derris 712% 
—tobacco dust 92'4%4%). Twenty-four hours later there were still 
a considerable number of live lice present, altho the number was very 
considerably reduced. Forty-eight hours after treatment the number 
was still further reduced. A second and a third dusting produced like 
results, the third practically removing all lice. 
A rat with a light flea infestation and a fairly heavy louse 
infestation was: isolated and treated with powder No. 2 as above. Re- 
sults were very similar to those obtained in the former experiment. 
No fleas were observed after the second application. It was noted, 
however, that the fleas that dropped from this rat very shortly after 
dusting seemed only stunned. Many of them recovered and were 
used to infect clean rats. It appears that the fleas endeavor to leave 
the treated rat to a certain extent. This may account for the faet 
that the dusting is not quite so effective in killing them as in killing 
the lice, and for the further fact that the second treatment completely 
cleared the treated rat. No attempt was made to trap the fleas. 
These two experiments are fair samples of all those made with 
powder of this strength. The powder is moderately effective in this 
dilution but not so much so as are the slightly higher concentrations. 
Powder No. 5 is similar to No. 2 in derris content but contains 
62%% tobacco dust and in addition contains 25% sulfur in a very fine 
state. The results of the trial were slightly more satisfactory than with 
the No. 2 powder, owing doubtless to the action of the sulfur. The 
following typical experiments show the usual results. 
A rat, infested with lice, was powdered as usual with five pinches 
of No. 5 powder. Twenty-four hours later the number of lice was 
very much reduced, the infestation remaining practically constant again 
after forty-eight hours. Twenty-four hours after the second treat- 
ment no lice were noted after a careful search. This rat was kept 
isolated and in a few weeks again developed lousiness, probably from 
the hatching of the numerous eggs contained in the fur. 
A second rat, lousy, and with a slight flea infestation, was treated 
as usual. Most of the fleas left the animal at once, dropping on the 
paper a few minutes after the powder was applied. These fleas seemed 
badly affected by the powder, but a fair percentage (approximately 
one fourth) recovered after a few hours. This rat was given no second 
treatment, as the first completely removed the fleas by either killing 
the insects or causing their migration. It was noticed, however, that 
