The essential task of higher education was enunciated by Premier Vulko Chervenkov in 1954: "Higher schools must train not only qualified specialists but also able, and conscious participants in the political direction and building of socialism in our country." In 1949 correspondence courses were initiated for manual workers and civil servants. Courses generally ranged from five to six years. Certain workers were allowed to attend shorter courses given by the various institutions while they continued to work. Although they were required to pass examinations, they did not have to attend classes regularly. Between 1948 and 1952 the curriculum became more and more patterned after the curriculum of the Soviet Union. In 1948 Marxist-Leninist studies were introduced; in 1949 political economy and the history of the Communist Party of the Soviet Union became obligatory for all university students. By 1950 the party newspaper, _Rabotnichesko Delo_, reported that 150 Soviet texts were being utilized in institutions of higher education. By 1952 students were obliged to study both dialectical and historical materialism, the rudiments of Marxism-Leninism, and the history of the BKP. Study of these subjects was generally mandatory for three years. In mid 1973 there were two major forms of higher educational institutions: teacher training institutions and university level institutions. In the latter category are universities, technical institutes, agricultural institutes, medical schools, art academies, and higher schools of economics. In 1972 there were twenty-two university level institutions, sixteen of which were in Sofia. The remainder were located in the provincial cities of Plovdiv, Varna, Svishtov, and Ruse. The courses of study range from four to six years; five years is the average period. In 1970 in proportion to the total population of the country, Bulgaria was fourth in the world in terms of the number of students--which constituted about 1 percent of the total population--attending institutions of higher education, following the United States, the Soviet Union, and Japan. Higher education in Bulgaria is conceived primarily in terms of the national economy. The entire educational process at the higher level is determined by the needs and prerequisites of the economy. The government has stated: "The main tasks of the institutions of higher education are: to train qualified specialists, imbued with Communist ideals, for all fields of activity, who will be conversant with the latest developments in science and technology, to train teachers and research specialists for the institutions of higher education and scientific organizations, to take systematic measures to improve the qualifications of specialists in various branches of the national economy; [and] to propagate scientific, technical and political knowledge among the workers."