SPRAYING FRUITS. 377 
In the case of most leaf-feeding insects, one should spray on the first in- 
dication of their presence. 
Caution necessary in the use of these insecticides—The relative suscepti- 
bility of apple, plum and peach has just been indicated under the head 
of arsenical poisons, and these remarks apply equally well to the use of 
the kerosene emulsions. In the case of other plants thorough experi- 
ments are still necessary, and all insecticides should be used in compara- 
tively high dilution. Tender-leaved plants, such as melons and cucum- 
bers, are more readily injured; while plants with firmer and smooth leaves, 
like the orange, are least affected. Annual plants, such as cabbages and 
other garden vegetables, are more susceptible than perennials; but in the 
case of root crops, such as beets, turnips, radishes, and potatoes, there is 
not the same need of caution as to damage to foliage. Damage to foliage 
is not shown at once, and in case of rain following an application another 
application should not be made for several days. Fruit trees should not 
be sprayed with arsenical poisons while in blossom, as there is no advant- 
age in doing so, and honeybees are reported to be at times killed by work- 
ing in the sprayed blossoms. 
SPRAYING FROM THE HYGIENIC STANDPOINT. 
The only insecticide sprays which are at all dangerous to use are the 
arsenic compounds, and even here the danger is greatly exaggerated by 
those not conversant with the facts. Paris green and London purple 
have for many years been extensively used in this country as insecticides, 
and a case of fatal poisoning from their use as such has never been sub- 
stantiated. The only danger lies in having the poison about a farm or 
plantation in bulk. Inthe early days of the use of Paris green against 
the Colorado potato-beetle a great deal of opposition was developed on 
account of the supposed danger, and only recently the sale of American 
apples in England has received a set-back owing to the supposed danger 
of arsenic poisoning from theirconsumption. The question as to whether 
arsenic may be absorbed by the growing plant in any degree was long ago 
settled in the negative by the best chemists in the country. Dr. William 
McMurtrie,formerly chemist of the Department, in 1878 showed that even 
where Paris green was applied to the soil in such quantities as to cause 
the wilting or death of the plants, the most rigorous chemical analysis 
could detect no arsenic in the composition of the plants themselves. 
Other experiments in a similar direction by Prof. R. C. Kedzie, of the 
Michigan Agricultural College, confirmed these conclusions. It is safe, 
then, to assume that the only way in which fruit or vegetables can convey 
the poison to the consumer will be through the very minute quantity of 
arsenic left upon the edible part of the plant. Against the possibility of 
such an effect the following facts may be urged: 
(1) It would seem at first glance that the use of an arsenical poison 
upon a plant like the cabbage would be very unsafe to recommend, yet 
Paris green and London purple are used upon this crop to kill the several 
species of leaf-eating worms which are so destructive to it, and an abso- 
lute absence of all danger,where tne application has been properly made, 
has been recently shown by Prof. Gillette, of the Agricultural Experi- 
ment Station of Colorado,. by the following reductio ad absurdum: 
* * * Where the green is dusted from a bag in the portion of 1 
ounce of the poison to 100 ounces of flour,and just enough applied to each 
