Considerations of the functions of the kidney have so long been centered preeminently on the elimination of water and of nitrogenous waste, and in lesser degree on inorganic constituents, that activities of the renal structures in other rôles have until recently had little interest directed to them. This tendency to minimize the importance of less familiar phenomena because others more often obtrude themselves on our attention is not unusual in science. The common features of every-day experience often engross us because of their frequent repetition and widespread occurrence, so that only the more discriminating and critical persons give heed to the lesser incidents in which, nevertheless, items of large significance may be hidden. Thus it has happened that the part played by the kidneys in regulating the neutrality of the body fluids has been little appreciated.
The outcome of the metabolism of the nutrients that serve as sources of energy