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. These divisions may be headed by deputy commissioners, but any deputy commissioner heading a medical division must be a medical doctor duly licensed in South Carolina. One of the divisions shall 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 shall be a Division for Long-Term Care which shall have primary responsibility for care and treatment of elderly persons who are mentally and physically handicapped to the extent that their needs are not met in other facilities either public or private.