1. Levin, M. B. and Raffel, S.: Gastric Digestion, a Simple Visual Test, and in Vitro Studies.Ann. Int. Med., Vol. 8, No. 7, Jan., 1935.
2. von Leube: Forchheimer’s Therapeusis of Internal Diseases, Vol. III, p. 123. Edited by Frank Billings, D. Appleton & Co., New York and London, 1916.
3. Lenhartz: Forchheimer’s Therapeusis of Internal Diseases, Vol. III, p. 123. Edited by Frank Billings, D. Appleton & Co., New York and London, 1916.
4. Sippy, Bertram W.: Handbook of Therapy, pp. 329–330. Oliver T. Osborne and Morris Fishbein, Eighth Edition,A. M. A., Chicago, Illinois.
5. Scott, Wilfred W.: Standard Methods of Chemical Analysis, pp. 255–369. Edited by Wilfred W. Scott, D. Van Nostrand Co., New York City, 1920.