42 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
seems to act both as a stomach poison and as a contact insecticide. 
Results obtained in the following experiments seem to indicate that 
it also possesses considerable toxicity for vertebrates. 
The liquid derris used was said to contain 16 per cent active derris 
and 84 per cent inert substances, the latter being for the grea‘er part 
apparently pyridine, which is probably used as the solvent for the 
derris resin. 
No analyses were made of the composition of the powder, largely 
because of the technical difficulties involved and because it would 
unquestionably vary considerably in different samples, owing to the 
manner of its manufacture. It is suspected, however, that it contains 
on the average between Io and 20 per cent of the active resin, the 
residue being cellulose, the debris of ground roots, etc. The powders 
were used as furnished by the By-products corporation and had the 
following compositions : 
Powder No. 1. Derris powder 10 %—Tobacco dust co % 
No. 2. Derris powder 734%—Tobacco dust 921%4% 
No. 3. Derris powder 100 %—Tobacco dust 00 % 
No. 4. Derris powder 20 %—Tobacco dust 80 % 
No. 5. Derris powder 714%—Tobacco dust 671%44% 
Powdered sulphur 25% 
The experiments were of two general types; those performed with 
the derris powder as furnished, and those with the liquid derris extract. 
The experimental animals were cats, dogs, white rats, and chickens; 
the insects being fleas, lice, chicken lice, and to some extent cockroaches. 
The fleas included the rat flea Ceratophyllus fasciatus Bosc., and the 
cat and dog fleas, Ctenophalus canis Curt. and C. felis Rothsc.. The 
chicken lice included both the body louse, Menopon biscriatum Paiget, 
and the head louse, Lipeurus heterographus Nitzsch., but especially the 
latter. The rat louse was the common louse of these animals, Polyplax 
spinulosus Burm. The cockroaches included the American roach, 
Periplaneta americana Linn., and the croton bug, Blatta gerimanica 
Linn. 
The experiments began with the use of white rats which were 
infested with the rat louse. It was found at once that a very slight 
amount of the powder was effective against the insects. It was ordi- 
narily applied by small pinches rubbed into the fur, usually two on the 
back, one on the belly, and two small pinches on the flanks—five in all. 
When used pure the powder (No. 3) acted with surprising rapidity, 
the animal usually being practically free of lice within a few hours 
(usually from three to five hours). In every case, however, where 
the pure powder was used the rats were sick on the following day; a 
