Frequency of micturition, especially if nocturnal, is often considered almost a proof of polyuria, but can at most only justify a presumption of it, which is to be confirmed or not by exact measurement. Any {28} existing polyuria is likely to be greater during the night. Frequency of micturition may mean polyuria, or, on the contrary, may coexist with a considerably diminished total amount of urine; in which case it means only increased irritability of the bladder, and is then a purely nervous symptom; assuming, of course, the absence of inflammatory trouble. The rapidity with which the secretion accumulates in the bladder has a certain influence in determining the need for micturition; that is, a bladder containing five ounces of urine which has been gradually accumulating for some hours retains it with greater ease than if the same amount had been rapidly secreted, as, for instance, after a full meal with an abundant supply of fluids. Polyuria is often, or always if persistent, an important symptom, and the suggestions made by it can easily be added to and confirmed by a more minute examination of the urine. Thus we may have the following combinations indicating important diseases: Polyuria, moderate, with diminished specific gravity, albumen usually in small amount, and some casts; in chronic interstitial nephritis; Polyuria, with pus and mucus and débris from the urinary passages, usually turbid and often alkaline and offensive; in irritation of the kidneys depending on lesions of the deeper urinary passages, prostate, or bladder (surgical polyuria); Polyuria, with increase of urea (azoturia); Polyuria, with increase of phosphates (phosphaturia); Polyuria, with increased specific gravity and sugar; in diabetes mellitus; Polyuria, with decreased specific gravity and diminished or normal solids; in diabetes insipidus. These conditions have many points of mutual contact and resemblance, but the affection which is the subject of the present essay is diabetes insipidus--_i.e._ that form of polyuria which is accompanied by no abnormal constituents except occasionally inosite, a very little sugar, or a very small amount of albumen. In the cases where these constituents might lead to difficulties in the way of diagnosis the absence of other symptoms of the disease likely to be mistaken will suffice to mark off the affection as entirely distinct. The normal elements may be decreased, normal, or increased. The disease thus defined includes not only diabetes insipidus, but many cases of so-called phosphaturia and azoturia, which, if not exactly coinciding, have many points in common.