In 1906, through the work of Voelcker and von Lichtenberg, the urinary tract was first rendered opaque to the roentgen ray. Since that time the technic of pyelography has steadily improved, and the procedure, now satisfactory and devoid of danger, plays a rôle of supreme importance in urologic diagnosis. The earliest efforts and their attendant difficulties are matters of common knowledge. The colloidal silver preparations of which so much was expected proved unsafe. Indeed, their untoward effects might well have been foretold had it been remembered how readily invasion of the renal and general circulations may follow abnormal pressure within the kidney pelvis. Instances of disaster following the use of silver are multiple, the damage resulting in most cases from silver embolism, and the kidney being usually the chief sufferer.
These more harmful substances,therefore, were supplanted by the thorium solution of Burns.1 This was an excellent contribution. Its value