IIYDATID OF THE LIVER.
of the liver is sometimes found in childhood. The disease sel dom occurs earlier than the fourth year of life, although Cruveilhier has quoted a case in an infant twelve days old, and M. Archambault has seen it in a child aged three years and a half. Between the fourth and eighth year it is sometimes met with, but is still rare. Alter the eighth year it is more common. The earliest age at which the disease has come under my own notice has been five years and a half.
Causation.—The hydatid grow Lh becomes implanted in the human liver as a result of the introduction into the stomach and intestines of the ova of the tocnia echinococcus. This creature is a parasitic worm inhabiting the alimentary canal of the dog and wolf. The tape-worm is a quarter of an inch in length, and has four joints, the last of which (the proglottis or sexually mature segment) contains the ova. The ova are excreted by the animal in whose intestines they have found a lodgment, and contaminating water or articles of food, become introduced into the human body. It is probable, also, that the ova and scolices may be sometimes conveyed to the child directly. In the dog, the presence of the worm in the bowels, and the passage of the eggs and embryos in large numbers through the anus, causes considerable irritation, which the animal endeavours to relieve by licking. If directly afterwards he apply his tongue to the face and mouth of the child, the parasite may pass at once to the child's tongue and be swallowed. How it travels from the alimentary canal to the liver is not clear.
Hydatid disease is endemic in Iceland, where the children are often af fected. The enormous number of dogs maintained on the island has been supposed, with much probability, to be the explanation of the frequency of the disease.
Morbid Anatomy.—Hydatid tumours are more common in the liver than elsewhere in the body ; but from the intestine they may pass not only into the liver but also into the spleen, the mesentery, the wall of the abdomen, and even into the substance of the heart and brain. The liver
may contain one sac or several. The sac itself consists of a firm fibrous capsule in close adherence to the liver substance, and is very vascular. Inside the capsule there is a clear gelatinous bladder (the envelope of the vesicle) composed of numerous fine concentric strata. This is the mother sac. It contains numerous large and small vesicles floating in a clear fluid, or adherent to the investing envelope. Some of the larger of the daughter vesicles may contain smaller sacs still of a third generation. These are seldom larger than the head of a medium-sized pin. The mother sac itself varies in size from a pea to a marble, an orange, or a child's head. The fluid it contains is non-albuminous and holds in solution salts, principally the chloride of sodium. On careful examination of this fluid, the booklets of the embryos (scolices) of the tmaia echinococcus may be often recog nised by the microscope.
The scolices themselves may be sometimes found. These are from one twentieth to one-sixth of a line in length. The head, which resembles that of the tmnia, has four suckers and a trunk. The latter is encircled by a double crown of hooklets, the number of which varies, according to Kuchenmeister, from twenty-eight to thirty, or from forty-six to fifty-two. The head is separated from the body by a groove, and at its posterior end is a depression into which a cord is inserted. This attaches it to the inner wall of the sac. The shape varies according as to whether the head is stretched out or retracted. On the body, elongated lines are seen passing backwards from the head. These are intersected by transverse striae. Besides these markings, a number of rounded calcareous corpuscles can be detected. The scolices lie in groups on the inner wall of the cyst, and can be seen through the vesicular wall as delicate white particles. Some times the mother sac contains scolices but no daughter resides. Some times it contains neither vesicles nor embryos.