The obligation of a dream was as binding as the necessity of fulfilling a vow, and disregard of either was said to be punished by the forces of nature, usually by a stroke of lightning. Dreams were sought by the Sioux, but it was recognized that the dream would correspond to the character of the man. Thus it was said that "a young man would not be great in mind so his dream would not be like that of a chief; it would be ordinary in kind, yet he would have to do whatever the dream directed him to do." The first obligation of a dream was usually its announcement to the tribe. This was by means of a performance which indicated the nature of the dream and allied the man to others who had similar dreams. If the dream were connected with the sacred stones, or with herbs or animals concerned in the treatment of the sick, it was considered obligatory that the man avail himself of the supernatural aid vouchsafed to him in the dream, and arrange his life in accordance with it.
Below will be found three groups of dream songs which, as noted among Chippewa as well as Sioux, are songs believed to be super- naturally received in dreams. The first of these groups comprises the songs of the Heyo′ka (dreamers of the thunderbird) and songs of those who dreamed of birds or animals. The numbers of these songs are 37-58, inclusive; with few exceptions they were recorded by the men who received them in their dreams. Two other groups follow; these comprise songs of the sacred stones and songs connected with the treatment of the sick.
A dream of the thunderbirds1 was considered the greatest honor which could come to a man from a supernatural source, and for this reason the obligation of the dream was heavier than that of any other.
The manner in which the thunderbirds are regarded was indicated by Shooter, who said:
Dreamers have told us of these great birds in the sky, enwrapped in the clouds. If the bear and other vicious beasts are regarded as dangerous, how much more should we fear the thunderbirds that cause destruction on the face of the earth. It is said that the thunderbirds once came to the earth in the form of giants. These giants did