The Department of Mental Health may be divided into such divisions as may be authorized by the director of Mental Health and approved by the commission. One of the divisions must be a Division on Alcohol and Drug Addiction which shall have primary responsibility in the State for treatment of alcohol and drug addicts. One of the divisions must be a Division for Long Term Care which shall have primary responsibility for care and treatment of elderly persons with mental and physical disabilities to the extent that their needs are not met in other facilities either public or private.