Various investigators have shown that columnar and transitional epithelial linings in certain organs of the body are capable of extensive epidermization when a protective covering is desirable. Broders1 has found a transition from a columnar to a squamous covering in everted, prolapsed irritated uteri. Rokitansky2 describes a stage of epidermoid metaplasia of the mucous membrane of the urinary bladder as cholesteatoma. Kretschmer3 collected from the literature the reports of forty-four cases of leukoplakia of the bladder, ureter, and pelvis of the kidney, showing that the urinary tract, normally lined by transitional epithelium, is capable of developing a squamous-cell surface. The traumatized exposed surfaces of extrophied bladders practically always show areas of epidermization.
Hallé4 holds that this epithelial transformation of the mucosa of the urinary passages results from chronic inflammation, either simple or due to stones. He reports seven such cases in the bladder, in all of