SCIENCE AND INDUSTRY. 
liquids have time to penetrate the chitin or the spiracles into the tissues. 
The nervous system of the insect is affected by the penetration of the 
‘volatile substance, and results resembling narcosis are produced where 
there is a disturbance of the respiratory activity. The insect tissues 
soon become saturated when exposed to the vapours, and death ensues 
through the inability of the tissues to absorb oxygen in the presence 
of these vapours. (Mich. Ag. Col. Tech. Bulls. 11 and 21.) In the 
case of lime sulphur, its effectiveness is due to its reducing power, and 
with scale insects to its softening action on the wax about the margin 
of the scales, and to its effect on the waxen covering making it less 
permeable to oxygen. Carbon disulphide, hydrocyanic acid gas, sodium 
fluoride, &c., act strongly on the oxidases and other enzymes in the 
tissues of insects, causing serious changes. The non-volatile finely 
powdered solids, such as borax and sodium fluoride, as well as being 
stomach poisons, are effective contact poisons, adhering to exudations 
on the body, and later becoming dissolved are absorbed through the 
integument into the tissues. 
Aphids, and other plant lice, bugs, and mites attack the under sur- 
face of the leaves, as this is probably easier to penetrate. By the sucking 
of the rich sap materials from the cells on the under side, the leaves 
curl somewhat, and so form a protective enclosure. Plant lice are so 
small that the grower often overlooks them and underestimates the 
damage that they cause. In attempting to control such pests with con- 
tact insecticides it will be understood that it is essential to spray the 
under sides of the leaves well, and a coarse, driving spray like nicotine 
can be used. 
Although the list of insecticides and fungicides is very extensive, 
those in greatest demand for spraying may be summarized as follows :—- 
Fungicides. 
1. Copper compounds (e.g., Bordeaux and Burgundy) especially 
valuable as winter sprays and as preventive sprays in 
early spring. 
2. Sulphur and its compounds.—Some are used with soap, suche 
as ammonium polysulphide, potassium sulphide (liver of 
sulphur) and sodium sulphide. One which is both fungi- 
cidal and insecticidal—lime sulphur solution—is not used 
with soap. 
Insecticides. 
Arsenical compounds (e.g., lead arsenates, Paris green) 
used as stomach poisons for biting and chewing insects. 
Nicotine (or tobacco extract) used against sucking insects. 
. Oils and emulsions (kerosene, red oil, creosote, and distil- 
late oils). 
3. Miscellaneous Methods and gases, fumigants and repellents, 
which need not be mentioned here. 
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OU He 
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When we attempt to combine certain preparations we are imme- 
diately faced with the greatest difficulty that the grower is likely to 
meet, viz., the unknown nature of the many proprietary and commercial 
preparations on the market. He will have to learn how to make a few 
simple tests for himself, such as the test for the presence of free copper 
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