[Footnote 6: Schrader, l.c.; see also Ihring, in _Deutsche Rundschau_, III., 357, 420; Kulischer, Der Handel auf primitiven Kulturstufen, in _Zeitschrift fuer Voelkerpsychologie und Sprachwissenschaft_, X., 378. _Vide post_, p. 10.] [Footnote 7: W. Bosworth Smith, in a suggestive article in the _Nineteenth Century_, December, 1887, shows the influence of the Mohammedan trade in Africa.] PRIMITIVE INTER-TRIBAL TRADE. Long before the advent of the white trader, inter-tribal commercial intercourse existed. Mr. Charles Rau[8] and Sir Daniel Wilson[9] have shown that inter-tribal trade and division of labor were common among the mound-builders and in the stone age generally. In historic times there is ample evidence of inter-tribal trade. Were positive evidence lacking, Indian institutions would disclose the fact. Differences in language were obviated by the sign language,[10] a fixed system of communication, intelligible to all the western tribes at least. The peace pipe,[11] or calumet, was used for settling disputes, strengthening alliances, and speaking to strangers--a sanctity attached to it. Wampum belts served in New England and the middle region as money and as symbols in the ratification of treaties.[12] The Chippeways had an institution called by a term signifying "to enter one another's lodges,"[13] whereby a truce was made between them and the Sioux at the winter hunting season. During these seasons of peace it was not uncommon for a member of one tribe to adopt a member of another as his brother, a tie which was respected even after the expiration of the truce. The analogy of this custom to the classical "guest-friendship" needs no comment; and the economic cause of the institution is worth remark, as one of the means by which the rigor of primitive inter-tribal hostility was mitigated.