What is the test for determining whether a chauffeur is a "servicant" to a defendant, and if so, is he liable for damages?

In McNamara v. Leipzig, supra, the owner of an automobile, for an agreed price, rented the same to the defendant, and furnished the services of a chauffeur, for the period of three months. The car was to be used by the defendant at any hour of the day or night as desired by him. The owner agreed to pay the wages of the chauffeur, to furnish all gasoline and supplies, and to pay for all repairs to the automobile. It was held that the chauffeur was not the servant of the defendant, and that the defendant was not liable for damages caused by his negligence. The court said: