In recent years an enormous amount of painstaking scientific investigation and persistent, praiseworthy effort have been expended on the part of such masters as Koranyi, Kümmell, Casper, Israel, Rovsing, their assistants, and many others, with a view to finding and elaborating a reliable method of determining the functional activity or possibilities of each kidney separately, or of both kidneys combined, in advance of a contemplated or possible nephrectomy. The result of all this investigation and effort has been to add one after another to the already long and still growing list of so-called functional tests. Yet despite the fact that every recent writer on the subject, with or without personal experience in the matter, feels himself called on to discuss at greater or less length all and sundry of the various functional tests of which he may have heard or read, it can not be said that anything even approaching