er will get a good understanding of the
relative positions of the kidneys, bladder, and adjacent organs.

THE KIDNEYS.

It is hardly necessary to discuss the minute structure of these organs
in a book intended for the non-professional reader.

The function of the kidneys is to remove certain waste materials from
the blood. As fast as excreted by the kidneys, the urine passes through
the ureters, of which there are two,--one leading from each kidney, into
the bladder. The ureters are lined with a continuation of the mucous
membrane, reflected from the bladder upwards, and this lining also
extends to the cavities of the kidneys.

Calculi or gravel, and stones, forming, as they sometimes do, in the
kidneys, and passing down through these delicate and sensitive canals,
cause excruciating pain. The symptoms of renal calculi passing from a
kidney to the bladder are, as already indicated, severe cutting pain in
the loins, and along the ureter, attended with considerable fever. A
very rough stone, such, for instance, as a mulberry calculus, passes
with considerable difficulty, and the patient is often suddenly seized
with excruciating agony in the loins and in the groin, the pain also
shooting down into the testicle of the corresponding side, often causing
it to retract. There is usually, also, sympathetic pain shooting down
the thigh. We have seen patients roll on the floor in the greatest
agony, cold sweat meanwhile pouring down their faces, when thus
suffering. The patient may also vomit violently, through nervous
sympathy. The urine is apt to be bloody, and there is a constant desire
to pass it. There is pain in the end of the penis, and also in the lower
portion of the abdomen.

THE BLADDER.

This is a sac, or reservoir, to receive and hold the urine as it comes
from the kidneys through the ureters. Its walls are partly composed of
muscle, and partly of a lining mucous membrane. The muscular coating is
external, and it is by its contraction that the urine is expelled. When
empty, the bladder shrinks down to a small size, as compared with its
distended condition. When filled, it is capable of holding about one
pint. If it is distended by the retention of urine much beyond this
capacity, the muscular coats lose their force, and often the urine
cannot be passed naturally. In health, when the bladder becomes filled
and distended, there is a consequent desire to empty it by passing
water.

[Illustration: Fig. 1.]