42 CFR 136a.41: a.41 Definitions.

For purposes of making appointments to vacancies in all positions in the Indian Health Service a preference will be extended to persons of Indian descent who are:

(a) Members of any recognized Indian tribe now under Federal jurisdiction;

(b) Descendants of such members who were, on June 1, 1934, residing within the present boundaries of any Indian reservation;

(c) All others of one-half or more Indian blood of tribes indigenous to the United States;

(d) Eskimos and other aboriginal people of Alaska; or

(e) Until January 4, 1990 or until the Osage Tribe has formally organized, whichever comes first, a person of at least one-quarter degree Indian ancestry of the Osage Tribe of Indians, whose rolls were closed by an act of Congress.