In the human subject it is not common for more than one
cyst to be present in the body at the same time, though
occasionally many are present — an unaccountable fact which
is worth remembering in giving a prognosis and in under-
taking treatment.
The cyst may lie in any part of the kidney and pushes the
kidney substance aside, producing a fibrosis limited to the
neighbourhood of the cyst. Three layers may be distinguished :

1. A false, thin outer capside formed of fibrous connective-
tissue and kidney substance, well supplied with blood-vessels.
2. The tnce outer chitinous capside of the cyst, which is a
quarter of an inch thick, stout but friable, and of a charac-
teristic opaque, bluish-white colour.
3. The inner parenchymatous layer of the cyst, which is
lined by scolex heads and booklets, and may produce daughter-
cysts.
The contained fluid is opalescent, of low specific gravity
(1004 to 1014), contains a trace of albumen, sodium chloride,
and toxic bodies, which are very irritating if allowed to
escape into the tissues, and may give rise to urticaria and
general toxic symptoms. Innumerable daughter-cysts may
be present, lying free in the cyst cavity or attached to the
inner wall. The microscope reveals the presence of the
characteristic hydatid booklets and embryonic scolex heads.
Complications.
1. The cyst may Imrst and discharge its contents ; in the vast
majoi'ity of cases it bursts into the ureter, and the daughter-



CrSTS OP THE KIDNEY. 217

cysts are discharged into the bladder ; rarely it bursts into
the lung, peritoneum, gut, and on to the skin.
2. Suppuration in the cyst,

3. The fluid may dry up, the walls become calcified, and the
contents sterile.
4. llie cyst may cause pressure on important structures in
its neighbourhood.
