A pesticide produced by the Degesch company, initially designated exclusively for eradicating insects. From the end of the summer of 1941, it was also used sporadically to put to death Auschwitz I prisoners and Soviet POWs; from the spring of 1942 it was used regularly to murder Jews in the Birkenau gas chambers. It took the form of granules of diatomaceous earth saturated with hydrogen cyanide, which was released at an appropriately high temperature (approx. 27 degrees C) and turned into a gaseous form. Its application produced so‑called internal asphyxiation of the victims by blocking the exchange of oxygen in the red corpuscles and impeding cellular respiration. At least 25 tons of Zyklon B were delivered to Auschwitz in the years 1942–1944. According to postwar testimony by Rudolf Höss, it took from five to seven kilograms of the pesticide to murder fifteen hundred people.