Fumigation of large areas with prussic acid, as we know it today, is nonetheless quite properly a war invention: exactly 25 years ago *) in 1916, the first attempts at delousing large mills and military barracks with prussic acid took place, which then led in 1917 and 1918 to increased employment of this procedure in military hospitals, barracks and ultimately to the development of delousing measures, already meaningful in the First World War. Since then, application techniques and procedures have been significantly changed and improved. Today, Zyklon Prussic Acid is known as the "method of choice" as M. Kaiser says**), not only for getting rid of bugs and delousing, but generally for the fumigation of large areas all over the world.

To a previously unimaginable extent, this procedure has been brought into play in this war for the fumigation of military barracks; already in the first months after the beginning of the Polish campaign, above all however, in the fall and winter months of 1940/41 following the fighting in France, millions and millions of cubic meters of lodging areas had to be rid of bugs by gassing with Zyklon prussic acid, to make secure for our soldiers the peace in winter they deserved. And in the weeks in which we now live, there is still a use for prussic acid fumigation that, given the extent of the newly occupied territories in the east, will surpass the previous work both in number and extent.

Normally it comes to pass that the major part of fumigation activities declines in the fall and winter months, which, given the special conditions in Russia, correctly raises the question as to whether, in respect of the expected low temperatures, the fumigation procedures are too much to expect. It is known that the efficacy of all gassing procedures on pests and their brood is to the greatest degree dependent upon the temperature, so that for example for T-gas procedures, the lower limit of +15°C and for tritox procedures, +6 to 8°C cannot be exceeded. At lower temperatures, the efficacy of these gases is doubtful.

Quite obviously this question is timely even though already fundamentally tested through numerous practical fumigations as well as laboratory experiments. At those times the questions asked were different in respect of fumigations, and were whether at low temperatures

1. prussic acid still evaporated quickly enough and completely from the carrier material and whether the gas wasn't so significantly adsorbed into the cold walls of the room that strong gas losses occurred;

*) Zeitschrift für das gesamte Getreidewesen 1941 (28) 9, page 117: W. Rasch "25 Jahre Blausäure-Durchgasungen".
**) Wiener Klinische Wochenschrift 1939 (52) page 45: M. Kaiser "Zweck und Ziele der gesundheitlichen Überwachung größerer Menschenmengen aus seuchenverdächtigen Gegenden (Fleckfieberabwehr mit Zyklon-Verfahren)