Pritchett, C. Herman, author
University of North California Press, 1943
Buku Teks
White, Leonard D., author
Macmillan, 1955
Buku Teks
Waldo, Dwright, author
Random House, 1965
Buku Teks
Scmidt-Bleek, F
Tenn. Center for Business and Economic Research University of Tennessee, 1972
Buku Teks
Univ. of Tennessee
The health and safety dept., 1973
Buku Teks