Except as otherwise provided herein, the persons specified in Sec. 31.11 shall be entitled to medical, surgical, and dental treatment and hospitalization only at medical relief stations and by designated physicians and designated dentists, and the cost of services procured elsewhere shall not be borne by the Service. (Sec. 610(b), 58 Stat. 714, as amended; 33 U.S.C. 763c)