206 FLAT WORMS. 



Man contracts the infection from association with dogs. The 

 disease is peculiarly prevalent in Iceland. As stated above, the adult 

 stage is passed in the intestine of the dog. Should the egg-bearing 

 segments passed by the dog contaminate the hands of man and a single 

 egg be ingested, we may have hundreds of Taenia larvae produced. 

 The 6-hooked embryo, leaving its shell, bores its way through the walls 

 of the alimentary tract and especially seeks the liver, just as the 

 onchosphere of the T. solium seeks the brain and eye. 



In the development of the cyst, after the onchosphere has come to 

 rest at some point in the liver, we have formed at first an indistinctly 

 laminated external envelope with coarsely granular fluid contents. 

 Later on the contents become transparent, and 2 distinct layers can be 

 observed: (i) The external, markedly laminated one, and (2) the 

 internal one, made up of small cells externally and large cells and cal- 

 careous corpuscles internally. This internal lining membrane is 

 known as the parenchymatous or germinal layer. When the external 

 layer is incised it curls up by reason of its elasticity. This is character- 

 istic of such a cyst. In addition, we have an enveloping connective- 

 tissue capsule formed by the surrounding liver substance. From the 

 germinal layer arise the brood capsules and the scolices. In these 

 brood capsules we have the cellular layer external just the reverse of 

 the mother cyst. Scolices may develop either on the outside or inside 

 of these brood capsules. It is interesting to note that one onchosphere 

 may develop hundreds of scolices. From the parenchymatous layer 

 of the mother cyst, daughter cysts are formed; these have an external 

 stratified layer and an internal parenchymatous one; within them a 

 varying number of scolices may develop. From these daughter cysts, 

 granddaughter cysts may arise all within the mother cyst- and 

 hence are termed endogenous. 



At times the daughter cysts work their way external to the mother 

 cyst and proceed to develop in a manner similar to the endogenous 

 formation. The exogenous development is rare in man, but common in 

 hogs. Hydatids containing no scolices are called sterile. These cysts 

 may be as large as a child's head, but are usually smaller. The fluid of 

 these cysts contains about i% of NaCl, also a trace of sugar; in addition 

 there is a toxin which produces urticaria and acts as a cardiac depress- 



