Addis, Thomas (1881–1949), American physician. Addis is most notable for his work in pathology and in particular for the study of kidney function. In 1925 he presented his method for counting cells in urinary sediments. The resultant figure is used to diagnose pathological conditions in the kidney and is now known as the Addis count. He is also known for his test, first reported in 1922, for determining the specific gravity of the urine. Addis's other areas of research included blood coagulation, hemophilia, plasma, and glycosuria.