Erwin E. Nelson, the pharmacology consultant who directed the New Drug Section beginning in 1947, was promoted to Medical Director after Stormont's departure. Ralph Smith became the Chief of the New Drug Section after Nelson moved up, a position Smith held until the mid-1960s. Both an M.D. and Ph.D., Smith came to the FDA from the Tulane University School of Medicine, where he served as chairman of the Pharmacology Department. Under Smith's leadership, the agency approved over 7,000 New Drug Applications. Soon after the ascendancy of Nelson and Smith, Congress passed another law with a significant impact on drug regulation. The Durham-Humphrey Amendment of 1951 clarified the vague line between prescription and nonprescription drugs theretofore under the law. The Amendment specifically stated that dangerous drugs, defined by several parameters, could not be dispensed without a prescription, witnessed by the prescription legend: "Caution: Federal law prohibits dispensing without prescription."