PYRETIIRUM AS USED AGAINST THE COTTON WORM. Ib9 
owe the first accurate determination of the destroying principle in Py- 
rethrum. He wrote us as follows on this subject: 
I have bad Milco's product in baud for some time, and bave tried it on various bugs 
botb in powder aud infusion. To understand tbe best maimer of using it in each 
case, it must be kept in mind : 
1. Tbat tbe active substance is a volatile oil. 
2. That said oil, under tbe influence of air, not only volatilizes, but is also oxidized, 
and thereby converted into an inert resin. 
It follows l'rurn 1 tbat the pyre-thrum is at a disadvantage when used in the shape 
of powder in the open air, especially when the wind blows; from 2 that it is of tin- 
greatest importance that the substance should be fresh, or should have been kepi 
tightly packed, for the same reason that bops must be similarly treated. 
Hence I And that Milco's fresh powder is of greater efficacy than the best imported, 
although some of tbe latter contains twice as much matter soluble in ether; but the 
( xtraet from the "buhach" is a clear greenish oil, while that from imported powder, 
and especially that from " Lyon's magnetic ''—ground-up refuse, steins, &c, as I take 
it — is dark and thickish, or almost dry and crumbly. 
The real nature of the effect of this volatile oil on insect life has not 
yet been studied, and still remains obscure. Different species ot 
insects are differently affected by the powder, but since no other 
animate are affected so far as we yet know in anything like the same 
degree, it may be interred that with insects those organs are affected 
which are essentially characteristic of them, viz., those connected with 
respiration. Some insects resist the action of the powder to quite a 
marked degree, e. (j., very hairy caterpillars, and especially spiders of 
all kinds; while others, especially all Ilyinenoptera, succumb most 
readily. In no case are the insects killed instantaneously by Pyrethrum. 
They are rendered perfectly helpless a few minutes after the applica- 
tion, but do not die till some time afterward, the period varying from 
several hours to two or even three days, according to the species. 
Many insects that have been treated with Pyrethrum show signs of 
intense pain, while in others the outward symptoms are much less 
marked. 
The effect of Pyrethrum on the Cotton Worm may be described as 
follows: The worm becomes uneasy in from 5 to L'O seconds after the 
application, according to the amount of Pyrethrum applied, and, again, 
according to the size of the worm. Very shortly afterward it attempts 
to bite off or to remove the particle or particles of the powder adhering 
to its body, during which operation a greenish juice emanates from its 
mouth. Its motions become more and more violent, until at last, within 
from 4 to 10 minutes, the whole body is thrown into convulsions, the 
worm having lost all control over itself. These convulsions continue 
for many hours, the worm getting weaker and weaker until death ensues. 
Small worms die in about 3 or 4 hours ; half-grown ones often not before 
24 hours have elapsed. Full-grown worms are not easily affected, and 
generally recover from the effects of even a pretty strong dose of Pyre- 
thrum, while very young worms are most! readily affected even by a very 
