284 THE NATURE AND TREATMENT OF 



ject more and more into the parent cell, and at last become 

 detached from its wall, and lie loosely within it. Shortly be- 

 fore this separation, however, the young hydatid is seen to 

 contain smaller cells, which increase in size along with it. 

 This increase continues until the new brood thus formed 

 entirely fills the cavity of the parent, and a farther increase 

 causes the rupture of the sac and the escape of the progeny ; 

 and these in their turn undergo the same evolution, becoming 

 parent hydatids in distinct cysts, and setting free their contained 

 cells as a subsequent generation. These cystic entozoa are 

 never found in the alimentary canal, but are always embedded 

 in the liver, brain, or glands of organs. They obtain their 

 food by absorption from the inner surface of the investing 

 membrane. Hydatids infest the various organs of the bodies 

 of all mammalia, and, although they are said to possess an 

 independent existence while residents of the organ or organs 

 which they inhabit, they die immediately when removed from 

 their chosen habitation. 



" * The principal genera of cystic entozoa are — cysticercus, 

 coenurus, echinococcus ; to which may be added acephalocystis. 

 Several species of cysticercus are enumerated, but the most 

 common are cysticercus tenicollis and cysticercus cellulosus. 

 The former (taenia hydatagenia, hydatis globosa) is met with 

 frequently in the peritoneum and pleura of ruminating animals 

 and pigs. It is often generated in the disease called rot, where 

 another entozoon, the distoma or fluke worm, is met with in 

 the biliary ducts (liver). The cysticercus cellulosis is found 

 generally lodged in the tissues of the muscles ; it occurs some- 

 times in man, but mor^ frequently in animals, particularly in 

 the hog, where it causes the disease denominated measles. Of 

 the genus coenurus (hydatis polycephalus), the species cere- 

 bralis is found in the brain of the sheep, oxen, and other 

 ruminating animals. These hydatids on the brain of sheep 

 cause the disease called sturdy, or giddiness. The hydatids 

 belonging to the genus echinococcus are considered by some 

 as varieties of the acephalocyst. They are commonly called 

 ♦ Pan, in the London Field. 



