EXPERIMENTS WITH PYRETHRUM. 21 
were lying helpless upon the table, although still retaining considerable 
vitality. In twenty hours they were dead. 
EXPERIMENT NO. 7.—EXPERIMENT UPON LARVA OF DATANA MIN- 
ISTRA. 
This experiment was conducted in the same manner as Experiment 
No. 4. Three full-grown larve of Datana ministra were placed in each 
of nine tin boxes and sprinkled in the same manner with the same 
amount of the different poisons. The boxes this time, instead of being 
covered with their own tight tin covers, were covered with slabs of glass, 
which, on account of the irregularities in the edges of the boxes, did not 
fit tightly, and allowed for a pretty free circulation of air. But this per- 
haps was compensated for by the fact that the covers did not have to be 
lifted to observe the condition of the larve. - The fact should be remem- 
bered in comparing this experiment with No. 4. The following table 
shows the result, and it will be noticed that the Datana is susceptible 
in a remarkable degree to the action of the pyrethrum when compared 
with Hyphantria or Plusia: 4 
