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carefully, one by one, as to the degree of their infestation, using, 
for convenience, a scale of ten degrees. One such grading should be 
made and recorded at the time the trees are sprayed, another about 
the last of May, just as the young are beginning to appear, and a 
third at the end of fall, when multiplication of the scales has vir- 
tually ceased for the season. All the grading should be done by 
one person, or by two persons independently, their estimates being 
averaged, and the person grading the infestation should not know 
the particulars of the experimental treatment. 
A comparison of the average degrees of infestation of the checks 
when the spray is applied, and again in May, will show the extent 
to which the scales may have died during the interval, under the 
effects of weather or from other causes, and a comparison of the check 
and experimental plots, respectively, in May, will show the immedi- 
ate effect of the insecticide. A similar comparison of these two 
kinds of plots, made at the end of the season of multiplication, will 
show the ultimate effect of the treatment at the end of the year. 
Original Purpose of Operations. 
Our own operations were originally planned with special refer- 
ence to the comparative values of modifications of the lime and sul- 
phur mixtures proposed by various entomologists, and also as a 
preliminary test of the efficiency of soluble petroleums, lime and sul- 
phur solutions, and other ready-made commercial products fre- 
quently offered for sale. Reports made by my field parties of the 
partial failure of midwinter sprayings with the lime and sulphur 
washes led me also to provide for a careful test of the final effect of 
sprays applied in January as compared with those applied in March. 
Most General Results. 
The main general outcome of these experiments was to establish 
still more firmly the lime and sulphur washes as superior, on the 
whole, to all the other mixtures tested, and to show that January 
applications of these preparations have scarcely more than half the 
final effect of applications made in March. Among the lime and sul- 
phur mixtures, those made without salt or blue vitriol seemed clearly 
more efficient, as insecticides, than the older forms containing those 
substances, and the solutions made with soda, without boiling, were 
the least efficient of all. 
