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(2- to 3-week hunger stage) were subjected to prussic acid in concentrations of 2-4 g CN per cbm. The temperature was varied and kept, in one experiment, at exactly 0°, and, in a second, between -6 and 8°. The bugs gassed were exposed before the gassing to the respective test temperatures, some for a shorter duration, some for longer (1-25 hours), in order to approximate the effects of warming (the different durations of this pretreatment were not significant as shown by the results).

In the well-known way, the necessary threshold values for 100 percent mortality and therewith the sought after gram-hour (gh)-values were determined. With inclusion of earlier test results for normal room temperatures, the following overview arose from the experiment:

Development stage  18 to 20°   -6 to -8°

Larvae 2 gh 7 gh ca. 12 gh
Adult Insects 4.5 gh 6-7 gh ca. 10 gh

The difference in the sensitivity between larvae and adults could still be unequivocally determined at low temperatures. Strange to say, this difference shifts in the direction that the larvae, which when warm are unequivocally more resistant than adult animals, appear when cold to lose capacity for resistance compared to the adult animals.

As the most important result of these experiments, it can be established that the gh-values required at low temperatures are well beyond the limit that can be guaranteed through the practically determined gas concentrations attained with normal dosages. Even at the normal dosage of 10 g/m3, a certain killing of all bug forms is to be expected down to about -10°C. At greater cold, the same can be guaranteed through correspondingly increased concentrations.

Final Results.

The experimental results reproduced in this paper bring certainty to the assumption, grounded in the experiences of the war winters 1939/40 and 1940/41, of the certain effect of prussic acid on bugs at low temperatures. What however can now be claimed with certainty about killing bugs can also be valid for the control of fleas less resistant to prussic acid and clothing lice very sensitive to cold. It must properly be expected that prussic acid fumigation can again prove its superiority for large-scale fumigations of all kinds, even in the especially different conditions of the Russian winter.