y even fill the bladder. Sometimes the nucleus of a
calculus is a chip of bone or a blood-clot, or some foreign substance
which has been introduced into the bladder. Sooner or later the urine
becomes alkaline and the calculus is encrusted with lime salts.

When urine contains a larger amount of chemical constituents than it can
conveniently hold in solution, a certain quantity crystallizes out, and
may be deposited in the kidney or in the bladder. If the crystals run
together in the kidney the resulting concretion may either remain in
that organ or may find its way into the bladder, where it may remain to
form the nucleus of a larger vesical calculus, or, especially in the
case of females, it may, while still small, escape from the bladder
during micturition.

In children, in whom there is a rapid disintegration of nitrogenized
tissues, a uric acid calculus in escaping from the bladder may block the
urethra and give rise to sudden retention of urine. On introducing a
metal "sound," the surgeon may strike the stone, and if it happens to be
near the bladder he may push it back and subsequently remove it by
crushing. But if it has made its way some distance along the urethra, so
that he can feel it from the outside, he should remove it by a clean
incision.

A stone in the bladder worries the nerves of the mucous membrane, and,
giving them the impression that the bladder contains much water, causes
the desire and need for micturition to be constant. The irritation
causes an excessive secretion of mucus, just as a piece of grit under
the eyelid causes a constant running from the eye. So the urine, if
allowed to stand, gives a copious deposit. During micturition the
contracting bladder bruises its congested blood-vessels against the
stone, so that towards the end of micturition blood appears in the
urine. Lastly, cystitis occurs, and the urine contains fetid pus. A
stone in the bladder gives rise to pain at the end of the penis, and it
is apt suddenly to stop the flow of urine during micturition.

The association of any of these symptoms leads the surgeon to suspect
the presence of a stone in the bladder, and he confirms his suspicions
by introducing a slender steel rod, a "sound," by which he strikes and
feels the stone. Further confirmation may be obtained by the help of the
X-rays, or, in the adult, by using a cystoscope. In a child the stone
may often be felt by a finger in the rectum, the front of the bladder
being p