References

Children's Britannica. (1988). Fourth edition/Vol.1/pp.46-47. U.S.A.: Encyclopedia Britannica, Inc.

Encyclopedia Britannica. (1975). Volume 1/p.72. U.S.A.: Encyclopedia Britannica, Inc.

The New Illustrated Medical and Health Encyclopedia. (1959). Volume 1/pp.38-39. New York City: H.S. Stuttman co., Inc.Publishers.

World Book Encyclopedia. (1995). Volume 1/p.54. Chicago:World Book Inc,.

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