DERRIS AS A PARACITICIDE 45 
the louse infestation was again very much reduced. There is no doubt 
that the No. 5 mixture is considerably more efficient than the No. 2 
containing the same percentage of derris. 
A rat heavily infested with lice was treated with the No. 1 
powder (containing 10% derris and go% tobacco dust). The effec- 
tiveness of this powder was about equal to that of No. 5 so far as lice 
were concerned, possibly a little more efficient, but two treatments 
were necessary to clear the infested animal. Upon continued isolation 
infection again appeared in about the same time (two to three weeks) 
as in the animals treated with the No. 2 powder, due again probably 
to the hatching of the eggs in the fur. 
A rat lightly infested with fleas was treated. This treatment 
was apparently more efficacious than the No. 5 treatment, the fleas 
leaving the animal but very few surviving after doing so. One treat- 
ment completely cleared the animal of fleas, and it is calculated that 
about 90% of those found on the paper did not survive. No count 
was made, the paper containing the fleas being placed over a rat cage 
in order to save the live fleas for further use. 
The best results were obtained with powder No. 4. This powder 
contains 20% derris and 80% tobacco dust. A lousy rat treated with 
this powder showed no appreciable number of live lice after twenty- 
four hours. A second, examined after twenty-four hours, showed 
a few exceedingly sluggish lice. An isolated animal did not show 
‘reinfestation within two weeks and a half, when it was returned to 
the general hutch for reinfestation. This animal, the same that had 
been treated about a month previously with No. 2 powder, did not 
carry a large number of eggs, altho a few were noticeable on the 
fur at the time of treatment with the No. 4 powder. 
A flea-infested rat was treated, and again the rat was flea-free with- 
in twenty-four hours. Apparently none of the fleas that dropped off 
this rat within the first five minutes recovered. Upon making a second 
test on another rat, of the seventeen fleas dropped off in the first 
five minutes none had recovered twenty-four hours later. These fleas 
were placed under a bell jar after being counted. This rat was given 
a rather heavy treatment, the pinches being generous, and since the 
animal was a large one, seven pinches were applied. It was acci- 
dentally returned ‘to the flea-infested hutch immediately after treat- 
ment. This hutch had a moderate infestation with fleas, and a grow- 
ing crop of larvae. Three days later a rat was removed for examination 
and no fleas were found. Altho it is not certain, it is probable from 
the results of later experiments that the powder retained in this rat’s 
