8

      As all the experience of workers in America and South Africa goes to show
that even delicate plants are not injured by the gas when present in sufficient
concentration to clear them of insects, the answer would be that it is not injurious.
An experiment we did confirmed this. Certain amounts of the above grains
subjected to the gas were planted, and their growth compared with control grains
which had not been fumigated. No difference in the rate of growth could be
detected. So during a fumigation, stored dry grain can be left in the house.
without fear of rendering it poisonous or of destroying its germinating power.

     Unlike Sulphur dioxide gas hydrocyanic acid gas has no action on metals
or fabrics.

The action of the gas on bacteria.

     About 4.38 cubic feet of diluted gas were introduced into a room of capacity
830 cubic feet and allowed to act for twenty minutes on bacteria. Cultures of
streptococci, Bacillus typhosus, Bacillus coli, and Bacillus pestis on agar slopes
in test tubes with their cotton-wool stoppers removed were put in the room.
After the experiment subcultures on agar showed that the plague was overgrown
with a yellow contaminating organism. The other bacteria had not been killed by
the action of the gas.

     This coincides with the experience of the Government Entomologist of the
Cape of Good Hope as noted in the Report for 1901: "Cultures of the plague.
bacillus were found to be unaffected when exposed by substituting a piece of
gauze tied over the top for the plug of cotton-wool ordinarily used for stopping
culture tubes by one hour in 1 to 80 gas—the severest test employed."

Disinfection for plague.

     Its harmless effect on the plague bacillus does not condemn hydrocyanic
acid gas as a preventive for the spread of plague. Preventive measures for
this disease fall under two heads :—

         (1) Disinfection of clothing of railway and other travellers. This is
equivalent to the destruction of plague germ carriers, namely, fleas.

         (2) Disinfection of plague houses. This is equivalent to the destruction
of plague rats and of plague fleas.

I.—The use of hydrocyanic acid gas for the disinfection of clothing.

     There is no question of its great efficiency, its cheapness, and the rapidity
with which the operation can be carried out—all matters of importance. It has
further the advantage of having no destructive effect on fabrics.

     Our experiments were carried out in two ways :—

     (a) First method.—Potassium cyanide was mixed with sulphuric acid and
water (1 of sulphuric acid to 19 of water) at first in glass flasks and in later