Frequently in Central and Northwestern California there is some more or less public ceremony at which a new shaman is, so to speak, initiated before he practices his powers. The body of initiated shamans do not form a definite society or association. The ceremony is rather an occasion that marks the first public appearance of the novice, in which he receives for his own good, and presumably for that of the community also, the assistance of the more experienced persons of his profession. Commonly it is thought that the novice cannot receive and exercise the full use of his powers without this assistance. The ceremony is usually held in the ceremonial chamber and is accompanied by dancing. The efforts of the older shamans are directed toward giving the initiate a firm and permanent control of the spirits which have only half attached themselves to him and which are thought to be still more or less rebellious. Of course exhibitions of magic and of the physical effects of the presence of the spirits are a prominent feature of these ceremonies. This initiation of doctors is found among the Northwestern tribes and in the Central region among the Maidu and Wintun and probably other groups. A special class of shamans found to a greater or less extent among probably all the Central tribes, though they are wanting both in the Northwest and the South, are the so-called bear doctors, shamans who have received power from grizzly bears, often by being taken into the abode of these animals--which appear there in human form,--and who after their return to mankind possess many of the qualities of the grizzly bear, especially his apparent invulnerability to fatal attack. The bear shamans can not only assume the form of bears, as they do in order to inflict vengeance on their enemies, but it is believed that they can be killed an indefinite number of times when in this form and each time return to life. In some regions, as among the Pomo and Yuki, the bear shaman was not thought as elsewhere to actually become a bear, but to remain a man who clothed himself in the skin of a bear to his complete disguisement, and by his malevolence, rapidity, fierceness, and resistance to wounds to be capable of inflicting greater injury than a true bear. Whether any bear shamans actually attempted to disguise themselves in this way to accomplish their ends is doubtful. It is certain that all the members of some tribes believed it to be in their power. The rattlesnake doctor, who cured or prevented the bite of the rattlesnake, was usually distinct from other medicine-men. Among the Yuki his power, as that of the rattlesnake, was associated with the sun; among the Maidu with the thunder. Among the Yokuts the rattlesnake shamans annually held a public ceremony designed to prevent rattlesnake bites among the tribe. On this occasion they displayed their power over the snakes by handling them in a manner analogous to that of the Hopi, and by even allowing themselves to be bitten.