THE TAPEWORM LARV^ 213 



Tabular Review of Life History of Echinococcus Granulosus 

 Adult Tapeworm. — In intestine of dog. 



Egg. — Expelled from intestines. 



Embryo. — Released from egg in digestive tract after 

 I ingestion by pig, ruminant, or other 



I mammal. 



Mother Vesicle (Hydatid). — In liver or other organ of 

 I same. 



Daughter Vessicles 



Scoleces. — ^Attached to intestinal wall of dog 

 I after ingestion of brood capsules con- 

 I taining larval heads. 

 Adult Tapeworms. — -In intestine of dog. 



Regarding the longevity of the hydatids, such information as is pos- 

 sessed is furnished mainly by cases of hydatid disease occurring in man. 

 A case is recorded of the persistence of an echinococcus cyst in a horse 

 for seven years. Usually when foiuid in lower animals it is in those 

 slaughtered for food, and in most such cases the animals are not old 

 enough for the hydatids to have reached their full development. It is 

 probably for this reason that the disease is cKnically unobserved or is 

 much less serious in these animals than in man where the hydatid devel- 

 opment remains uninterrupted. 



The himian evidence seems to indicate that the longevity of the cyst 

 may be only limited by that of its host, for a case is recorded where it 

 had existed for thirty-five years and another where the swelling had 

 gradually spread over the face for forty-three years, and when operated 

 upon had attained the size of a child's head. 



Post-mortem Appearance.^Hepatic echinococcosis is accompanied 

 by considerable alteration. When the cyst is large the liver becomes 

 hypertrophied and its weight may be increased as much as ten times 

 that of normal. The increase in volmne may compress neighboring 

 organs, hindering their function and displacing them. The diaphragm 

 especially is crowded and pressed forward upon the lungs. The surface 

 of the liver has protruding elevations of various size and number, and 

 Glisson's capsule is noticeably thickened, perhaps forming adhesions 

 with contiguous organs. Section of the organ reveals cavities of un- 

 equal size from which the hydatic liquid with contained vesicles flows 

 out. The connective tissue capsules of the cysts will vary in thickness 

 from 3 to 10 mm, (1/16 to 3/8 of an inch). These capsules are structurally 



