“ Sec. 2. The functions vested in the President by Section 437 (b) of Title 18 of the United States Code (94 Stat. 544; Public Law 96-277) to prescribe rules and regulations under which any officer, employee, or agent of the Indian Health Service may purchase from or sell to any Indian any service or any real or personal property or any interest therein, are delegated to the Secretary of Health and Human Services. ”