258 i.V HYDATinS. 



specific characters.* Hydatids, like intestinal 

 "worms, are incapable of independent existence, and 

 therefore exhibit a contractile power, only when 

 examined immediately on being discharged from a 

 living animal. 



"The remaining for many hours within the 

 dead body generally deprives them of the princi- 

 ple of life ; and hence all specimens of hydatids 

 are not observed to contract; and such as retain the 

 power of contraction, for some time after being ex- 

 pelled, may be considered as unusually tenacious 

 of life. 



" Purulent matter, which is sometimes lodged 

 within the same viscus, also proves fatal to hyda- 

 tids ; and in this case, of course, they show no 

 contractile power. The hydatids, found in human 

 bodies, are different from those of quadrupeds. Of 

 "the humun hydatids, there are the following kinds. 



" 1. When there is only one large hydatid of 

 a globular form, contained within a cyst.f 



"3. Where there are several hydatids with- 

 in the same cyst, of different sizes and colours, 

 some being of a pearly, and others of a straw or 



* The generic name of hydria has been proposed, but no 

 character of tlie genus has been established. It seems not im- 

 probable thattlie hydatids of the human body must form a sepa- 

 rate genus, distinct from the hydatids of sheep. 



t See Case, VII, in which eight English pir^ts of fluid were 

 contained within a large hydatid ; there were no small hyda- 

 tids within it, and t!ie whole of the inner surface of the hyda> 

 tid was perfectly smooth. 



