The ability of the kidney to eliminate various substances administered either per os or parenterally has been practically employed by both the internist and surgeon as a means of determining its functional activity. The phenolsulphonephthalein test of Rowntree and Geraghty1 and the lactose and potassium iodid tests of Schlayer and Takayasu2 have found extensive use. More recently Neubauer3 has suggested the administration of creatinin as a functional test, since it is the one normal urinary constituent which is entirely endogenous and the rate of excretion of added creatinin may, therefore, be readily followed.
The functional condition of the kidney may be ascertained by two quite different modes of attack: by the amount of certain substances excreted by the kidneys, or by their retention in the blood. Since the introduction during the past two years of simple methods of blood analyses, especially at the