174 REPORT 4, UNITED STATES ENTOMOLOGICAL COMMISSION. 
shut up iu a tight tin box for 24 hours. This, blown by bellows, proved 
very efficient in destroying Aletia larvae which it touched." 
While it is thus proved that one part of Pyre thrum mixed with ten parts 
of flour and applied immediately after preparing, or the same amount 
of Pyrethrum to twenty parts of powder, applied after being kept in a 
tight vessel for some time, is sufficient to kill the average-sized worms, 
the problem yet remained to apply this mixture so that it would touch 
all worms on the plants. That this cannot be accomplished by an 
application from above is apparent from the habits of the older worms 
to hide, during the day, on the under side of the leaves, and even if ap- 
plied at night the mixture would, under the most favorable circum- 
stances, be but partially successful, as the young worms, which do not 
come at all to the upper surface of the leaves, would not be killed. Ap- 
plication from below is therefore imperative to insure success, and suit- 
able machines for this purpose will be described farther on. In the year 
1880 we estimated that it would require one and three-quarter pounds 
of Pyrethrum powder to go over an acre of cotton of medium height 
when mixed with 20 pounds of flour. With the improved appliances the 
amount per acre will probably be reduced to less than one x>ound. The 
price, when the first edition of this work was published, averaged 75 
cents per pound, but is much lower at the present writing. 52 
2. Application of pyrethrum in fumes. — Whatever advantages 
this method may have in a closed room it is evidently impracticable on 
a large scale in the field, and consequently no experiments have been 
made. 
3. Alcoholic extract of pyrethrum. — The not inconsiderable 
differences in the results obtained by the agents of the Commission 
while experimenting with extracts are principally due to the fact that 
the extracts can be obtained in various ways and of varying strength. 
A good extract may be obtained either by distillation or by the reperco* 
lation process. Which of the two methods is preferable it is difficult 
to say. The former seems, however, to more thoroughly extract the oil 
than the latter ; but in both kinds of extract the residuum of the powder 
may be kept in suspension so that no particle of the strength of the pow- 
der is lost. The extract by distillation is easily obtained by taking a 
flask fitted with a cork and a long and vertical glass tube. Into this flask 
the alcohol and pyrethrum are introduced and heated over a steam tank 
or other moderate heat. The distillate, condensing in the vertical tube, 
runs back, and at the end of an hour or two the alcohol may be drained 
off, and the extract is ready for use. 
Prof. E. A. Smith, of Tuscaloosa, Ala., found during the year 1879 that 
the extract thus obtained, if diluted with water at the rate of one part 
of the extract to 15 of water, and sprayed on the leaves, kills the worms 
that have come in contact with the solution in a few minutes. The 
mixture in the proportion of 1 part of the extract to 20 parts of water 
