46 NINETEENTH REPORT STATE ENTOMOLOGIST OF MINNESOTA—IQ22 
fur was distributed to the other three rats in the hutch as they lay 
sleeping together, and was finally scattered over the floor litter. [:x- 
amination of the litter showed a remarkable reduction in the number 
of live larvae present. This same accident happened twice during the 
experiments, the second one completely destroying the flea infestation, 
As a new flea culture was not obtainable, the experiments with 
fleas on rats were discontinued. However, some further work was 
done on stray cats and one experiment was made on a dog, all of which 
showed the 20% derris—80% tobacco dust mixture was very effective 
against fleas on these animals. The dog was treated by heavily dusting 
the rags in the box in which it slept. The method seemed completely 
effective against the fleas and also killed the few larvae contained in 
the old cloths. The work on cats was less satisfactory, as it was diffi- 
cult to apply the powder effectively to them since they were all rather 
wild and objected strenuously to being handled. 
Of the series of powders used, the No. 4 powder (derris 20%=— 
tobacco dust 80%) seemed to be the best combination. When used 
on rats pure derris proved fatal to the experimental animal in all but 
one case, in which it was used very lightly. While all the powders 
produced slight symptoms of illness in rats, none except the pure derris 
produced any permanent ill effects. The 20% derris completely re- 
moved both the louse and flea infestations in one treatment, and the 
fleas did not revive after dropping off the animal. From the results 
obtained by placing the treated rats immediately in the flea-infested 
cages it seemed evident that direct treatment of the infested animals 
was not absolutely necessary. A series of tests was made,. therefore, 
to determine if treatment of the nests or bedding was a practical method 
of eliminating the insects. 
Three rats heavily infested with lice were put in a clean cage 
with chip litter. Excelsior was used for nesting material and a small 
teaspoonful of derris powder No. 4 was shaken loosely into the excelsior. 
The rats quickly worked this over into a nest, spending most of their 
time beneath it. Examination two days later showed no appreciable 
infestation with lice. The rats were left in the cage about a month 
and showed no reinfestation until again placed with infested rats for 
reinfestation. The experiment was repeated several times with from 
one to three rats with essentially similar results. 
A similar experiment was tried with a small kitten harboring the 
cat flea, C. felis. Derris powder No. 4 was scattered over the old coat 
used as a bed for the kitten. This coat had a fair number of flea 
