The author examined 177 urinary calculi, which were obtained from 94 patients. The stones were examined chemically with especial reference to the quantitative values of the various urinary salts. Many stones were analyzed, after division into central, middle and outer layers; others were cut into sections from 0.2 to 0.02 mm. in thickness and studied microscopically. Various types present different important characteristics, particularly in regard to their surface, the size of the component crystals, and other interesting features of chemical interest.