P ordered from D machinery and equipment for $71,325.00. D was to install the machinery and equipment on P's premises for an additional consideration of $6,900.00. If P elected to install the machinery with its own labor, D would furnish a supervisor to direct the installation on a per diem basis. The order provided that 'the signing and returning of the Acknowledgment Copy by D to P shall constitute acceptance by Seller of this Purchase order and of all of its terms and conditions.' P submitted its order on printed forms regularly used by P. Item 15 of that printed form provided that if D was required to perform work on P's premises, D would be responsible for all damages or injuries occurring as a result of the fault or negligence of its own employees, including any damages or injuries to P's employees and property. Another indemnity provision was also attached by P which required the Seller to assume full responsibility not only for the fault or negligence of its own employees but also for the fault or negligence of P's employees, arising out of or in connection with D's work. This extra provision was marked 'VOID.' P then submitted its Amendment No. 1 to the purchase order, deleting the item of $6,900.00 for the cost of installation by D and providing that the installation would be done by P. These were accepted by D and the agreements were performed. Amendment No. 2 proposed to purchase additional machinery to be installed on P's premises by D, at a total cost of $173,700.00. Amendment No. 2, as did Amendment No. 1, provided: 'This purchase order agreement is not binding until accepted. Acceptance should be executed on acknowledgment copy which should be returned to buyer.' This time the extra provision was not marked 'VOID.' On this Amendment, the installation work on P's premises was to be performed by D's employees. The extra provision also stated, 'Such of the terms and conditions of Seller's Purchase Order as are inconsistent with the provisions hereinabove set forth are hereby superseded.' The second amendment was duly executed by D on or about November 10, 1956, and was received by P on November 12, 1956. But D had already begun installation of the machinery before the agreements were signed. On September 5, 1956, an employee of D, sustained personal injuries as a result of the negligence of D's employees. That employee sued P. P added D, as a third-party defendant, relying upon the indemnity provisions of the extra provision. D's injured employee got the verdict against P for $12,500.00. D appealed from the denial by the District Court of its motion for judgment notwithstanding the verdict of the jury and entry of judgment against it in favor of P upon the third-party complaint. D claimed that the agreement was not in effect when the injury occurred. D claims it did not become bound by the provisions of the amendment until November 1956, when it actually signed and returned the acknowledgment.