94 
material is very similar to that of the preceding determinations. 
The arsenious acid was found at the rate of 40.1 parts per million, 
enough to give .2807 grains per pound of the apple peelings. One 
would thus have to eat about three and a half pounds of these peel- 
ings to get a grain of arsenic. 
Two grains of arsenic is a fatal dose, and one thirtieth to one 
tenth of a grain is a medicinal dose. For the first, one would have 
to eat seven or eight pounds of these apple peelings; and for the 
second, from two to seven ounces. While these facts are not at all 
alarming, they suggest discretion in the use of this insecticide and 
in the subsequent handling and disposal of the apples. We also 
need further experiment with various strengths of the spray and 
with various kinds and amounts of subsequent exposure of the fruit. 
Nevertheless, in view of the fact that apple peelings are rarely 
eaten in any quantity, I think that no hesitation need be felt to sub- 
stitute the arsenate of lead for the more usual insecticide sprays 
if the facts here given are borne in mind and duly allowed for. 
The Neutrai. Zone; in Sprawng Experiments. 
It has been customary in making field insecticide experiments to 
apply the chosen treatment to a certain area, leaving a correspond- 
ing area immediately beside it untreated, as a check, the utility of 
the treatment being determined by a comparison of subsequent con- 
ditions on these two tracts. Attention has already been called by 
Gillette,* Weed,t and myselft to the fact that the results of such 
experiments must be somewhat affected by the spread of insects 
from the so-called check plot to the experimental plot, but nothing 
has been done to demonstrate this proposition expejimentally, or to 
show just how important this mutual influence of check and ex- 
perimental plots may be. 
In the spraying experiment conducted in Orchard I., as above 
described in this article, the opportunity was improved to ascertain 
to what extent the curculios spread from one part of the orchard to 
another — to what extent, that is, one must guard against vitiation 
of results of spraying experiments by the spread of the curculios 
from unsprayed trees to those which have been sprayed. This or- 
chard, it will be remembered, was divided into two equal parts, each 
virtually square, on one of which all trees were sprayed four times 
with arsenate of lead, beginning May 6 and following at intervals 
of ten days thereafter, while the other part was left unsprayed as a 
check. The apples in this orchard were of the Ben Davis variety, 
and were harvested September 20. At this time all the apples 
*Bull. Q (1800), la. Ayr. Exper. Station, pp 383-3S4. 
+Bull. 23 (18W), Ohio Afrr. Exper. Station, p. 226; Agricul. Science, Apr., 1«90, p. <I7. 
t'-Arsenical Poisons for the Codling--nioth." Bull. 1 il887), Office State Ent. 111., p. '»; 
Fifteenth Report, State Ent. 111., p. 13. 
