Dorlands Medical Dictionary (28th edition) defines Chiropractic as:

A Science of Applied Neurophysiologic diagnosis based on the theory that health and disease are life processes related to the function of the nervous system : Irritation of the nervous system by mechanical, chemical, or psychic factors is the cause of disease; restoration and maintenance  of health depends on normal function of the nervous system.  Diagnosis is the identification of these noxious irritants and treatment is their removal by the most conservative method.