107 



upon being the cessation of the heart's action. As the young were 

 transparent when viewed by transmitted light, the motion of the 

 heart of Hving specimens was easily detected. 



Whale Oil Soaj). 



From the 19th to the 22d several experiments were tried by dip- 

 ping the leaves in a solution of whale oil soap, or brushing their 

 surfaces with it, but as the strength of the solution was not noted 

 in these preliminary trials, I need only say that they were in all 

 cases effectual. 



Experiment 10. — On the 23d a branch of a tree infested with 

 bark lice was dipped in a suds of whale oil soap containing a pound 

 to a gallon of water, and on the morning of the following day the 

 lice were all dead. Two days later, however, the leaves dipped in 

 this solution showed signs of injury, the margins of most of them hav- 

 ing blackened and dried up. Naturally the younger leaves at the 

 tip of the branch were most severely injured, some having been 

 almost wholly destroyed. On the 29th, nearly all the leaves had 

 fallen off this branch. 



Experiment 11. — On the 25th July, leaves were dipped in a solu- 

 tion containing a quarter of a pound of whale oil soap to the gal- 

 lon, and on the 20th the bark lice were mostly dead, only a small 

 percentage showing a feeble movement of the heart. 



Experiment 12. — The above experiment was varied by using a so- 

 lution double the strength just mentioned. On the following day 

 all the specimens examined were dead. 



Experiment 13. — On the 28th, experiment 12 was repeated with 

 identical results, all the bark lice being dead two days later. 



Experiment 14. — This was a repetition of experiment 11. The 

 twigs were not examined, however, until five days afterwards. At 

 this time, at least seventy-five per cent, of the bark lice upon the 

 leaves were dead and many which were not killed seemed to have 

 been driven from the leaves as if the soap suds were obnoxious to 

 them. This was shown by their having fixed themselves upon the 

 petioles and twigs, a fact not elsewhere observed so early in the 

 season. The leaves were again very slightly injured at their mar- 

 gins, and a few, perhaps, eventually fell before their time. 



Experiment 15. — A repetition of experiment 12. Five days after 

 treatment not a single living bark louse could be found upon a leaf 

 containing a hundred or so, all being brown and loosened, so that 

 a touch dislodged them. The leaves, however, were slightly black- 

 ened at the margins, and some were doubtless injured enough to 

 cause them to fall. 



The experiments with whale oil soap were, consequently, less 

 satisfactory than those with the kerosene emulsion, an application 

 of the suds, strong enough to effect the purpose, being very likely 

 to injure the leaves at least as much as the bark lice would have 

 done. 



