61 



5th. Scrubbing the limbs of a tree with a stiff brush, shortly' 

 after the Bark-lice have hatched out, will destroy them and remove 

 them from the infected surface; but no such mechanical appliance 

 can remove or otherwise affect the perfected scale, simply because it 

 sticks too tight, and is of too hard and solid a texture. 



6th. By scraping the bark with the edge of a knife or other sucli 

 tool, even the perfected scale may at any time of the year be removed 

 and destroyed. 



To give all the details of all the experiments that I have made., 

 bearing upon the above general rules, would occupy entirely too mucli 

 space and only weary the reader. But I may be pardoned, perhaps, 

 for giving the details of a few of them, and for particularizing several 

 facts obtained from other sources, in order that it may be seen upon 

 what kind of evidence my general conclusions are based. Each 

 statement is numbered, so as to correspond with the six general laws 

 already laid down. 



Statement 1st. — On June 12th, 1867, being eight da3^s after 

 the Bark-lice had hatched, and probably about four or five days after 

 they had become permanently stationary, I prepared some tobacco- 

 water, by boiling for three hours one part, by measure, of common 

 smoking-tobacco and seven parts of water, renewing the water as it 

 boiled away. This fluid I squeezed with a sponge over a badly in- 

 fested branch, so as to wet the whole of it thoroughly both above and 

 below, using no brush or swab of any kind, so as absolutely to elim- 

 inate the effects of mechanical friction upon the young Bark-lice. 

 I had previously pruned the branch so as to cut off all communication 

 with neighboring branches, except at its origin ; and of course I labeled 

 it and registered it in my Journal. From time to time through the 

 summer I examined it, and found the young Bark-lice apparently 

 growing as vigorously as on the rest of the tree. On October 30th 

 I cut off a portion of it, one foot in length and averaging one-third 

 of an inch in diameter, and examined the scales one by one under 

 a lens. This piece, be it observed, was so distant from the origin of 

 the branch which I had washed with the tobacco-water, that it was 

 very improbable that any amount of young Bark-lice could afterwards 

 have crawled out on to it from the other parts of the tree, even sup- 

 posing them to have retained their original powers of locomotion. I 

 found, on examining it, at least 200 scales containing good, plump, 

 healthy eggs, and about 400 that had either been completely gutted 

 by the Mites, or were undergoing that process. There were about 

 seven or eight scales from which no "anal sack'' had developed ; these 

 might possibly have been larvse killed by the tobacco-water, but I 



