Acupuncture is based on the theory of yin and yang, which are not absolute but relative. Yin and yang are the opposites that make the whole. Yin is conceptualized as being cold, dark and female. Yang is warm, light and male. Neither of them can exist in isolation. These two opposites are not stationary, but in constant motion.The interaction of yin and yang produces "Qi", the bipolar energy. Life is possible only because of the interplay between these forces. The body, mind and emotions are all subject to the influences of yin and yang. Each organ has an element of yin and yang within it. The histological structures and nutrients are yin, and the functional activities are yang. Some organs are predominantly yang in their functions, such as the liver, while others are predominantly yin, such as the kidney. Even though one organ may be predominantly yin (or yang) in nature, the balance of yin and yang is maintained in the whole healthy body because the sum total of the yin and yang will be in a balance. Historically, acupuncture points were believed to be the holes that allow entry into channels. These holes provide us gateways to influence, redirect, increase, or decrease body's vital substance, Qi, thus correcting many of the imbalances. The efficacy of acupuncture, especially for relieving pain, has been proved beyond doubt and is no longer a question today. According to the Gate Control Theory , pain signals pass through a number of high-traffic 'gates' in the spinal chord, as they move from the area of injury upward into the brain. Like a road or highway, these nerves can handle only a limited number of nerve signals at a particular time. Under normal circumstances, this gate is wide open and pain impulses get through very easily. But when acupuncture needling is carried out, another stream of non- painful impulse flow towards the spinal chord. This causes overcrowding at the gates, resulting in jamming. This competitive inhibition of pain impulses leads to an analgesic effect and no pain is felt at the level of brain. Chemical or humoral mechanisms are also involved in relieving pain. These substances, called endorphins, are present in the brain, spinal chord and the intestines. The pituitary responds to acupuncture by releasing this painkiller, into the blood and cerebro-spinal fluid. This indirectly decreases the pain by reducing the firing rate of the pain impulses by the nerves at a distance. This phenomenon is described as pre-synaptic inhibition . The electrical theory of acupuncture states that acupuncture works by influencing the electromagnetic field in the body. This electrical field influences the growth, maturation, and functioning of some types of cells. The body also continually generates tiny, but detectable electrical discharges. Studies have shown that there is a correlation between the electromagnetic fields in the body and the channels or meridians. Acupuncture points, which lie along the meridians, when stimulated, alter the amount of neurotransmitters, leading to an altered sensation of pain. The important effects produced by acupuncture are analgesic, sedative, homeostatic or regulatory (an effect important for the body to adjust itself to the external environment), immune- enhancing, tranquilizing __apart from mere sedation, and motor recovery in paralytic patients. Apart from controlling pain, acupuncture can treat a wide variety of common and uncommon disorders. It has been shown to improve the circulation of blood, decrease high blood pressure, stabilize the rhythm and stroke volume of the heart, control the secretion of the gastric acid, increase the production of red and white cells. It also stimulates the release of a variety of hormones that help body to respond to injury and stress. The following is a list of disorders that can be treated by acupuncture (World Health Organization data): Respiratory: Acute Sinusitis, Acute rhinitis, Common cold, Acute tonsillitis, Acute bronchitis, Bronchial asthma. Eye: Acute conjunctivitis, short sightedness (in children), Cataract (without complications). Mouth: Toothache, post extraction pain, Gingivitis (gum disease), Acute and chronic pharyngitis. Gastrointestinal Disorders: Hiccups, Gastritis, Gastric Hyperacidity, Ulcers, Colitis, Constipation, Diarrhea, and Paralytic ileus. Neurological and Musculoskeletal Disorders: Headache and migraine, Trigeminal neuralgia, Paralysis following stroke, Meniere's disease, Neurogenic bladder dysfunction, Nocturnal enuresis (bed wetting), Intercostal neuralgia (pain in the ribs), Cervicobrachial syndrome (pain radiating from neck to arm), "Frozen shoulder" or "tennis elbow", Sciatica, Low back pain and Osteoarthritis. In the United States, acupuncture is used frequently for the treatment of chronic pain conditions such as arthritis, bursitis, headache, athletic injuries, and post traumatic and post surgical pain. It is also used for treating chronic pain associated with immune function dysfunction, such as psoriasis (skin disorders), allergies, and asthma. Acupuncture is also found to be effective for the treatment of mind-body disorders such as anxiety, chronic fatigue, irritable bowel syndrome, hypertension, insomnia, menopausal symptoms, and depression. Acupuncture has become popular throughout the world in the past few decades. It is now recognized as a simple, safe, effective and economical form of therapy, besides being free from side effects. It has not only been used as an anaesthetic agent, but also in many diseases that are resistant to conventional forms of therapy. Some modern application of acupuncture is in the treatment of disorders such as alcoholism, addiction, smoking, and eating disorders.