Chinese physicians believed that diseases result from imbalances in two life forces, Yin and Yang, that flow through the body. Drugs and other treatments were intended to restore this balance. Hundreds of ancient herbal medicines, including iron for anemia, mercury for syphilis, arsenic for skin diseases, and opium, are still used in traditional Chinese medicine. Other Chinese medicines and techniques, including acupuncture, are now commonly used in Western medicine. Most Chinese medicine was based on a famous textbook, the Nei Ching, written by Emperor Huang Ti between 479 and 300 bc. Chinese physicians specialized in treating wounds, fractured bones, allergies, and other diseases. They diagnosed patients by asking questions about symptoms, diet, and previous illnesses, and by checking the patient's pulse.