64 



many of the young Bark-lice killed by the soap, I counted 422 dead 

 Bark-louse larvae still adhering to the bark, witli the "anal sacTc" not 

 at all developed, and most of them without even a "medial scale,"' 

 the great bulk of which must therefore have been killed by the soap 

 while still in the larva state. If we assume that 22 of these were 

 males — which is a rather large estimate — and deduct these from the 

 total, we get 400 female bark-lice killed by the soap, to 7 that sur- 

 vived the operation of the soap; or, which is the same thing, out of 

 the whole number of females 98^ per cent, killed. It is possible 

 however, though not at all probable, that the seven female Bark-lice 

 that survived might have been late-hatched individuals, that crawled 

 down, before they became stationary and after the soap was applied, 

 from the small, terminal twigs that I neglected to soap. In this, as well 

 as in the other three experiments already detailed, the portion of the 

 branch examined under the lens was altogether too far removed from 

 the main limb which was not soaped, to allow of any considerable num- 

 ber of Bark-lice crawling on to it from the main limb ; and besides, 

 when all these experiments were tried, the great bulk of the Bark-lice 

 had certainly become stationary. 



Dr. Mygatt tried the same experiment about the same time of 

 the year, but used a much weaker solution of soap, which seems not 

 to have been quite so effectual. "One tree," he informs us, "was 

 treated with soap-suds, two tea-cupfuls of soft soap to a pail of water. 

 Every part was wetted by immersing the ends of the branches and 

 using a syringe. The leaves and young growth became yellow, but 

 were not destro3-ed. A part of the lice were killed, probably half or 

 more." {Transactions Illinois State Agricidtural Society, I. p. 516.) 



On November 7th, 1867, the scales being now of course fully 

 matured, I made a still stronger solution of the same soap, namely 

 one part by measure of soap to four parts of water, and applied it 

 when warm with a very soft shaving brush to a branch prepared and 

 labeled as in the other experiments. On December 5th, I cut off a 

 portion of this limb and examined the scales under the lens. From 

 some cause or other, upon this limb, which was upon a different pan 

 of the same tree and not so badly infested, the Mites had not oper- 

 ated at all, so far as I could discover. After lifting and examining 

 several scores of scales, and finding that every one of them without 

 exception contained good plump, healthy eggs, I became fully satis- 

 fied that the soap had not in anywise affected the vitality of the eggs, 

 and did not think it worth while to continue the examination. The 

 weather during the whole of November had been remarkably mild and 

 genial and dry; and, from my experience with the eggs of this and 



