April 1933. By that time, many people who were not Nazi Party members were advocating for segregating Jews from the rest of German society. The Law for the Restoration of the Professional Civil Service, passed on 7 April 1933, forced all non-Aryans to retire from the legal profession and civil service. Similar legislation soon deprived Jewish members of other professions of their right to practice. It also barred Jews from teaching at universities. In 1934, the Nazi Party published a pamphlet titled "Warum Arierparagraph?" ("Why the Aryan Law?"), which summarised the perceived need for the law. As part of the drive to remove Jewish influence from cultural life, members of the National Socialist Student League removed from libraries any books considered un-German, and a nationwide book burning was held on 10 May. Violence and economic pressure were used by the regime to encourage Jews to voluntarily leave the country. Legislation passed in July 1933 stripped naturalised German Jews of their citizenship, creating a legal basis for recent immigrants (particularly Eastern European Jews) to be deported. Many towns posted signs forbidding entry to Jews. Throughout 1933 and 1934, Jewish businesses were denied access to markets, forbidden to advertise in newspapers, and deprived of access to government contracts. Citizens were harassed and subjected to violent attacks. Other laws promulgated in this period included the Law for the Prevention of Hereditarily Diseased Offspring (passed on 14 July 1933), which called for the compulsory sterilisation of people with a range of hereditary, physical, and mental illnesses. Under the Law against Dangerous Habitual Criminals (passed 24 November 1933), habitual criminals were forced to undergo sterilisation as well. This law was also used to force the incarceration in prison or Nazi concentration camps of "social misfits" such as the chronically unemployed, prostitutes, beggars, alcoholics, homeless vagrants, black people and Romani (referred to as "Gypsies"). Reich Gypsy Law The Central Office for Combatting Gypsies was established in 1929, under the Weimar Republic. In December 1938 Reichsführer-SS Heinrich Himmler issued an order for "combatting the Gypsy plague". Romanis were to be categorised in terms of their Roma ancestry as a racial characteristic, rather than their previous association as 'anti-social' elements of society. This work was advanced by Dr Robert Ritter of the Racial Hygiene and Population unit of the Ministry of Health, who by 1942, had produced a scale of ZM+, ZM of the first and second degree,