Initially we note that
[investigations by a social service agency of allegations of child sexual abuse are in the nature of governmental functions. Such activities are performed for the public good. Thus a county normally would be immune from liability for injuries caused by negligent social services employees working in the course of their duties. The General Assembly, however, has authorized counties through a statute to waive the defense *654of immunity for negligent actions that occur in the performance of governmental functions through the purchase of liability insurance. Under this law, . . the DSS, as a County agency; and the County employees may be liable for negligent or intentional actions carried out in the performance of their social services duties. McNeill v. Durham County ABC Board, 87 N.C. App. 50, 359 S.E.2d 500 (1987), modified on other ground, 322 N.C. 425, 368 S.E.2d 619, reh’g denied, 322 N.C. 838, 371 S.E.2d 278 (1988).
I. Defendant Cooper
 Plaintiff first assigns as error the trial court’s entry of judgment in favor of defendant Cooper based upon the public official defense. Plaintiff argues that in our prior opinion, see Coleman, supra, we established that defendant Cooper “does not have the status or protection of a ‘public official.’ ”
When a governmental worker is sued individually, or in his or her personal capacity, our courts distinguish between public employees and public officers in determining negligence liability. Harwood v. Johnson, 92 N.C. App. 306, 309, 374 S.E.2d 401, 401 (1988). A public officer sued individually is normally immune from liability for “mere negligence.” Id. An employee, on the other hand, is personally liable for negligence in the performance of his or her duties proximately causing an injury. Id.; Givens v. Sellars, 273 N.C. 44, 159 S.E.2d 530 (1968).
A public officer is someone whose position is created by the constitution or statutes of the sovereign. State v. Hord, 264 N.C. 149, 155, 141 S.E.2d 241, 245 (1965). “An essential difference between a public office and mere employment is the fact that the duties of the incumbent of an office shall involve the exercise of some portion of sovereign power.” Id. Officers exercise a certain amount of discretion, while employees perform ministerial duties. Discretionary acts are those requiring personal deliberation, decision and judgment; duties are ministerial when they are “absolute, certain, and imperative, involving merely the execution of a specific duty arising from *655fixed and designated facts.” Jensen v. S.C. Dept. of Social Services, 297 S.C. 323, 377 S.E.2d 102 (1988).
In our prior decision, we specifically stated that a violation of G.S. 7A-544, which provides for the protection of abused or neglected juveniles, “[could] give rise to an action for negligence.” 89 N.C. App. at 197, 366 S.E.2d at 8. In Coleman, defendant Cooper was classified as an employee of Wake County and as a result could be subject to liability in the performance of her official duties. Accordingly, the Coleman court reversed the trial court’s entry of summary judgment in favor of defendants Cooper and Wake County on the grounds of sovereign immunity. “Once an appellate court has ruled on a question, that decision becomes the law of the case and governs the question not only on remand at trial, but on a subsequent appeal of the same case.” N.C.N.B. v. Virginia Carolina Builders, 307 N.C. 563, 566, 299 S.E.2d 629, 631 (1983). Since the trial court’s entry of summary judgment in favor of defendant Cooper was erroneously entered on the grounds that she was a public official, we reverse and remand this cause for trial.
II. Defendant Wake County
 Plaintiff next contends that the trial court erred in granting defendant Wake County’s Rule 12(b)(1) motion to dismiss for lack of subject matter jurisdiction. Plaintiff argues that this court in Coleman, supra, previously “recognized that Wake County [had] waived sovereign immunity to the extent it purchased liability insurance.” Plaintiff contends that the liability of Wake County is “based upon respondeat superior for the negligence of defendant Cooper” and the “failure of the Defendant Wake County to have appropriate safety procedures.” Plaintiff contends that the Wake County Superior Court is the proper forum for this claim and that the trial court erred in holding that the claim should be brought before the Industrial Commission. We disagree.
A county’s liability for the torts of its officers and employees depends on whether the activity involved is “governmental” or “proprietary” in nature. Traditionally, a county was immune from torts committed by an employee carrying out a governmental function, but was liable for torts committed while engaged in a proprietary function. The North Carolina Supreme Court has distinguished between the two as follows:
*656Any activity ... which is discretionary, political, legislative or public in nature and performed for the public good in behalf of the State, rather than to itself, comes within the class of governmental functions. When, however, the activity is commercial or chiefly for the private advantage of the compact community, it is private or proprietary.
Often making this distinction proves difficult. Certain activities are clearly governmental such as law' enforcement operations and the operation of jails, public libraries, county fire departments, public parks and city garbage services. Non-traditional governmental activities such as the operation of a golf course or an airport are usually characterized as proprietary functions. Charging a substantial fee to the extent that a profit is made is strong evidence that the activity is proprietary. [Citations omitted.]
Under The Tort Claims Act the North Carolina Industrial Commission (Commission) is “constituted a court for the purpose of hearing and passing upon tort claims against the . . . departments, institutions, and agencies of the State.” G.S. 143-291. The Commission is authorized to determine “whether or not each individual claim arose as a result of a negligent act of any officer, employee, involuntary servant or agent of the State while acting within the scope of his office, employment, service, agency or authority, under circumstances where the State of North Carolina, if a private person, would be liable to the claimant in accordance with the laws of North Carolina.” Id.
Vaughn v. Dept. of Human Resources, 296 N.C. 683, 685, 252 S.E.2d 792, 794 (1979). “Under the Tort Claims Act, jurisdiction is vested in the Industrial Commission to hear claims against the State of North Carolina for personal injuries sustained by any person as a result of the negligence of a State employee while acting within the scope of his employment.” Guthrie v. State Ports Authority, 307 N.C. 522, 536, 299 S.E.2d 618, 626 (1983).
In Vaughn, supra, the claimant brought an action before the North Carolina Industrial Commission against the Department of Human Resources alleging that the Director of Durham County Social Services and five of his caseworkers were negligent in plac*657ing a foster child in her home carrying the cytomegalo virus when they knew that the claimant was attempting to become' pregnant. The Department of Human Resources moved to dismiss the action before the North Carolina Industrial Commission on the grounds that “the Durham County Department of Social Services is not a State department and the Director and employees thereof are not State employees within the meaning of G.S. 143-291.” Id. at 684, 252 S.E.2d at 794. The Full Commission and the Court of Appeals determined that the Industrial Commission had jurisdiction to hear and determine the claim. The Supreme Court allowed discretionary review.
In Vaughn, the North Carolina Supreme Court stated that “[i]n order for the Commission to assert jurisdiction over this claim there must be a showing that the Director of the Durham County Department of Social Services and his staff were acting as the ‘involuntary servants or agents’ of a ‘State Department’ under circumstances in which the State, if a private person, would be liable for the negligent acts of the named servants or agents.” Id. at 685, 252 S.E.2d at 794, citing G.S. 143-291. The Vaughn court further stated that “[application of the principles of agency law and respondeat superior to the statutory scheme for the delivery of foster care services leads us to conclude that liability may exist and that the Industrial Commission may therefore ‘hear and pass upon’ the merits of this claim pursuant to the provisions of the Tort Claims Acts.” Id. at 686, 252 S.E.2d at 795. We note that the Vaughn court stated that it “expressed] no opinion on whether the Department of Human Resources might also be liable for negligent acts of the County Director outside the scope of his obligation to place children in foster homes. In every instance the liability of the Department of Human Resources depends upon application of the principles of agency and respondeat superior to the facts in the case under consideration.” Id. at 692, 252 S.E.2d at 798, citing Snow v. DeButts, 212 N.C. 120, 193 S.E. 224 (1937).
G.S. 108A-1 requires that “[e]very county shall have a board of social services which shall establish county policies for the programs established by this Chapter in conformity with the rules and regulations of the Social Services Commission and under the supervision of the Department of Human Resources.” G.S. 108A-14(5) provides that the director of social services shall “act as agent of the Social Services Commission and Department of Human Resources in relation to work required by the Social Services Com*658mission and Department of Human Resources in the county[.]” G.S. 108A-14(11) further provides that the director of social services shall “investigate reports of child abuse and neglect and to take appropriate action to protect such children pursuant to the Child Abuse Reporting Law, Article 44 of Chapter 7A[.]” “The Director of the Department of Social Services shall submit a report of alleged abuse or neglect to the central registry under the policies adopted by the Social Services Commission.” G.S. 7A-548(a). The central registry of abuse and neglect cases is maintained by the Department of Human Resources. G.S. 7A-552. Finally, “a subordinate division of the state, or agency exercising statutory governmental functions like a city administrative unit, may be sued only when and as authorized by statute.” Smith v. Hefner, 235 N.C. 1, 6, 68 S.E.2d 783, 787 (1952).
In the instant case, Wake County was acting as an agent of the Social Services Commission and the Department of Human Resources in its delivery of protective services to the decedents. A cause of action originating under the Tort Claims Act against Wake County as a subordinate division of the State, must be brought before the Industrial Commission. Accordingly, the trial court did not err in dismissing the action against Wake County. Because we have affirmed the trial court on this issue, we need not address defendants’ cross assignment of error.
In summary, with respect to defendant Cooper, we reverse the entry of summary judgment in her favor and remand this cause for trial. With respect to defendant Wake County, we affirm the superior court’s dismissal of this action.
Affirmed in part; reversed and remanded in part.
Judge Parker concurs.
Judge ARNOLD concurs in part and concurs in the result as to defendant Cooper by separate opinion. ^