1. Goodpasture, E. W.: An anatomical study of senescence in dogs, with special reference to the relation of cellular changes of age to tumors. J. Med. Res., 38: 127–196, 1918.
2. Becker, W. F., Coleman, W. O., Powell, J. L., and Turner, R. J.: The age factor in acute cholecystitis. J. Louisiana State Med. Soc., 114: 1–6, 1962.
3. Crump, C.: The incidence of gall stones and gall-bladder disease. Surg. Gyn. & Obst., 53: 447–455, 1931.
4. Deaver, J., and Bortz, E. L.: Gallbladder disease, a review of 903 cases. J.A.M.A., 88: 619–623, 1927.
5. Fisher, H. C. and White, MacM. H., Jr.: Biliary tract disease in the aged. Arch. Surgery, 63: 536–544, 1951.