This is a prosecution for adultery committed on one of the Sioux Indian Reservations in the state of South Dakota. Both participants in the act were Indians belonging to that reservation. The statute upon which the prosecution is founded was originally adopted as part of the act of March 3, 1887 (chap. 397, 24 Stat. at L. 635), and is now § 316 of the Penal Code (Stat. at L. 1149, chap. 321, Comp. Stat. 1913, § 10,489 ). The section makes no mention of Indians, and the question for decision is whether it embraces adultery committed by one Indian with another Indian, on an Indian reservation. The district court answered the question in the negative.
...counsel for the government invite attention to the letter of the statute, and urge that adultery is not an offense 'by one Indian against the person or property of another Indian,' and therefore is not within the exception in § 2146 of the Revised Statutes (Comp. Stat. 1913, § 4149).

...And are they not intended to be in accord with the policy reflected by the legislation of Congress and its administration for many years, that the relations of the Indians among themselves-the conduct of one toward another-is to be controlled by the customs and laws of (U.S. 602, 606 ) the tribe, save when Congress expressly or clearly directs otherwise? In our opinion this is the true view.