A registered nurse, by reason of her professional character generally is considered to be an independent contractor in the performance of services in attendance upon private persons. This position is based on the theory that the nurse, after an extended period of prescribed and supervised training and the receipt of a certificate, holds herself out to the public as exercising an independent calling requiring specialized skill. A registered nurse performing services under the foregoing circumstances is an independent contractor. A registered nurse performing services in the employ of a hospital or similar institution, or in a physician's office, is subject to the direction and control of the employer and is an employee of the person for whom the services are performed.