The widely spread American custom of a youth acquiring a guardian spirit is far more prevalent among the southern section than the northern, but among the Kwakiutl he can only obtain as his patron, one or more of a limited number of spirits which are hereditary in his clan. In the northern tribes the secret societies are coextensive with the totemic clans; among the Kwakiutl they are connected with guardian spirits and it is significant that during the summer, when the people are scattered, society is based on the old clan system, but when the people live together in villages in the winter, society is reorganised on the basis of the secret societies. There is a highly developed system of barter of which the blanket is now the unit of value, formerly the units were elk-skins, canoes or slaves. Certain symbolic objects have attained fanciful values. A vast credit system has grown up based on the custom of loaning property at high interest, at the great festivals called "potlatch" and by it the giver gains great honour. The religion is closely related to the totemic beliefs; supernatural aid is given by the spirits to those who win their favour. The raven is the chief figure in the mythology; he regulates the phenomena of nature, procures fire, daylight, and fresh water, and teaches men the arts. To the south, and extending inland to the divide, forming a much less characteristic group are the Salish or Flat-heads who are allied to the Athapascans. The coastal Salish assimilate the culture just described, but the plateau Salish are more democratic, less settled and more individualistic in religious matters[821]. The Chinooks or Flat-heads of the lower reaches of the Columbia river are nearly extinct. They deformed the heads of infants. These tribes and the Shahapts or Nez Perces are differentiated by garments of raw hides, cranial deformation, absence of tattooing and plain bows, but they still have communal houses though without totem posts. They cook by means of heated stones and have zoomorphic masks[822].