It will be observed that, with the exception of oats, none of the grains contain more than two-thirds of the nitrogenous material present in the wheat bran, while in the case of rye and maize there is practically but one-half. Even in the case of oats the albuminoids, which are the more digestible principles, and therefore those that are the most easily and speedily converted into urea, are present only to the amount of two-thirds of that which exists in the wheat bran. With such an excess of ash, of phosphates, and of nitrogenous (urea-forming) constituents in wheat bran, its tendency to favor the formation of calculi is fully explained. It must not, however, be inferred that wheat bran is not a valuable feedstuff. The inference is only that it should be fed with an abundance of water, as a sloppy mash, or in combination with an abundance of roots, potatoes, pumpkins, or other succulent aliment. In this connection the presence of magnesia in the feed or water must be named as favoring calculous formations in the urinary passages. The explanation is that while the phosphate of magnesia thrown out in the urine is soluble in water, the compound phosphate of ammonia and magnesia is insoluble, and, accordingly, if at any time ammonia is introduced into urine containing the phosphate of magnesia there is instantly formed the ammonio-magnesium phosphate, which is as promptly deposited in the solid form. The common source of ammonia in such cases is from decomposition of the urea in fermenting urine. In order to produce this a ferment is necessary, however, and therefore, as an additional prerequisite, the presence of bacteria, or fungi, in the urine is essential. These ferments may make their way from without along the urinary passage (urethra), and their propagation in the bladder is greatly favored by the prolonged retention of urine, as in case of spasm of the neck of the bladder or obstruction by an already existing stone. Another mode of entrance of the ferment is an unclean catheter used to draw the urine. Still another is the elimination through the kidneys of the bacteria of infectious diseases, or of such as, without producing a general infection, yet determine fermentation in the urine. The precipitation is favored not only by the production of ammonia, but also by the formation of viscid (colloid) products of fermentation. In this sense bacteria are most important factors in causing gritty deposits in the urine.