The causes of this affection are similar to those of the preceding.

Gravel probably originate in the kidneys, and finding their way to the bladder through the ureter, there become gradually enlarged until calculi are formed. More can be done for the relief of stone in the bladder by regulating the diet than by the use of any of the so-called "solvents" for calculi, which are of little, if any, value. Large calculi generally require a surgical operation for their removal. The cutting operation so long practiced is now being, in a considerable degree, superseded by the new operation of crushing, which can be performed by a skillful surgeon much more rapidly and safely than the old operation of lithotomy.