"HUMAN ECHINOCOCCUS.'' 159 



animals. Pallas, in 1760, recognised them as parasites, 

 and showed their close connection to the tapeworm 

 a discovery which was confirmed and extended by 

 Goeze shortly afterwards. The first accurate description 

 however, of a " Human Echinococcus " was given by 

 Bremser in 1821, who traced the relationship of a 

 hydatid to the tapeworm ; and it is now recognised more 

 or less in all countries by those who have read the able 

 works of Von Siebold and Frerichs, that the echinococcus 

 is nothing more nor less than the " embryo " of a tape- 

 worm, which immigrates in that form into the liver, and 

 there assumes the form of tapeworm by gradual develop- 

 ment, and enters the intestinal canal as such. 



ANATOMICALLY. The anatomy both microscopically 

 and otherwise of the hydatids and echinococci, are 

 marvellously interesting, and given with great minute- 

 ness both by Frerichs and Eokitanski, which are here 

 briefly embodied, in the following description : 



1. Hydatid, or the Acephalocyste of Laennec. This 

 consists externally of a firm fibrous capsule, of a 

 whitish tint, intimately adherent to the surrounding 

 glandular tissue, and freely supplied with a shower of 

 branches of the hepatic artery, and portal vein. 

 Within this fibrous sac or capsule is enclosed a soli- 

 tary, independent and thoroughly distended bladder, or 

 vesicle, containing a limpid serous fluid the so-called 

 mother-sac of the echinococcus ; that is to say, in its 

 earliest stage or Kmbryonic form. Within this parent 

 sac are found floating about other and similar vesicles 

 of various sizes and numbers. In size they vary from 

 a poppy or millet seed, or homoeopathic globule, to 

 that of a goose's egg, and sometimes even to a greater 



