was launched no later than 2 September 1939 and existed until the end of the war with 39 subcamps. It is estimated that 65,000 Poles were murdered there. The total number of Polish nationals who were murdered in the camps, prisons and places of detention inside and outside Poland exceeds 1,286,000. There were special camps for children such as the Potulice concentration camp, the Kinder-KZ Litzmannstadt for Polish boys, and the forced-labour camp for Polish girls at Dzierżązna (Dzierzazna). Auschwitz became the main concentration camp for Poles on 14 June 1940. By March 1941, 10,900 prisoners were registered at the camp, most of them Gentile Poles. In September 1941, 200 ailing Polish prisoners along with 650 Soviet POWs, were murdered in the first gassing experiments with Zyklon-B. Beginning in 1942, Auschwitz's prisoner population became much more diverse, as Jews and other "enemies of the state" from all over German-occupied Europe were deported to the expanding camp. Franciszek Piper, the chief historian of Auschwitz, estimates that 140,000 to 150,000 ethnic Poles were brought to that camp between 1940 and 1945, and that 70,000 to 75,000 were murdered there as victims of executions, human experimentation, forced starvation and disease. Instances of pseudo medical experiments occurred. For example, 74 young Polish women were subjected to medical experiments on bone and muscle transplantation, nerve regeneration and wound infection in the Ravensbrück concentration camp. Sulfanilamide experiments were conducted on Polish Catholic priests in Dachau. More than 300 Polish priests were murdered in experiments or by torture. Already in 1939, the Germans divided all Poles along the ethnic lines. As part of the expulsion and slave labor program, Jews were singled out and separated from the rest of civilian population in the newly established ghettos. In smaller towns, ghettos served as staging points for mass deportations, while in the urban centers they became instruments of "slow, passive murder" with rampant hunger and dead bodies littering the streets. The ghettos did not correspond to traditional Jewish neighborhoods. The ethnic Poles and members of other groups were ordered to take up residence elsewhere. The Warsaw Ghetto was the largest ghetto in all of Nazi occupied Europe, with over 400,000 Jews crammed into an area of , or 7.2 persons per room. The Łódź Ghetto was the second largest, holding about 160,000 inmates. By the end of 1941, most of about 3.5 million Polish Jews were already ghettoized, even