Despite a government crackdown, the number of private ambulances is growing. The Chinese medical education system is based on the British model. While some medical schools run three-year programs, hospitals tend to recruit physicians who graduated from five-year programs, while big-name hospitals only accept MDs, which takes seven years of study, including the five years of undergraduate studies, followed by the completion of a PhD in medicine. Once a student graduates from medical school, he or she must work 1–3 years in a university-affiliated hospital, after which the student is eligible to take the National Medical Licensing Examination (NMLE) for physician certification, which is conducted by the National Medical Examination Center (NMEC). If the candidate passes, he or she becomes a professional physician, and is certified by the Ministry of Health. It is illegal to practice medicine in China as a physician or assistant physician without being certified by the Ministry of Health. Physicians are allowed to open their own clinics after practicing medicine for five years. China has one of the longest recorded history of medicine records of any existing civilization. The methods and theories of traditional Chinese medicine have developed for over two thousand years. Western medical theory and practice came to China in the nineteenth and twentieth centuries, notably through the efforts of missionaries and the Rockefeller Foundation, which together founded Peking Union Medical College. Today Chinese traditional medicine continues alongside western medicine and traditional physicians, who also receive some western medical training, are sometimes primary care givers in the clinics and pharmacies of rural China. Various traditional preventative and self-healing techniques such as qigong, which combines gentle exercise and meditation, are widely practiced as an adjunct to professional health care. Although the practice of traditional Chinese medicine was strongly promoted by the Chinese leadership and remained a major component of health care, Western medicine gained increasing acceptance in the 1970s and 1980s. For example, the number of physicians and pharmacists trained in Western medicine reportedly increased by 225,000 from 1976 to 1981, and the number of physicians' assistants trained in Western medicine increased by about 50,000. In 1981 there were reportedly 516,000 senior physicians trained in Western medicine and 290,000 senior physicians trained in traditional Chinese medicine. The goal of China's medical professionals is to synthesize the best elements of traditional and Western approaches. In practice, however, this combination has not always worked smoothly. In many respects, physicians trained in traditional medicine and those trained in Western medicine constitute separate groups with different interests. For instance, physicians trained in Western medicine have been somewhat reluctant to accept unscientific traditional practices, and traditional practitioners have sought to preserve authority in their own sphere.