On and after May 9, 1938, the Secretary of the Interior is authorized, in his discretion and under such rules and regulations as he may prescribe, to make advances to old, disabled, or indigent Indian allottees, for their support, to remain a charge and lien against their land until paid; such advances for the fiscal year 1939 to be made from the appropriations in this paragraph and those for fiscal years thereafter to be made from appropriations specifically available for such purposes.