14 



The cyst of the Echinococcus is contained, either singly or in num- 

 bers, in the interior of a cavity lined with an organized false mem- 

 brane, to which it has no kind of adhesion whatever. It is found of 

 all sizes, from that of a pin's head to many inches in diameter, and 

 the thickness of the walls bears some, but no definite relation to the 

 size of the bag, and in the larger cysts is not uniform. When re- 

 cent, the cyst is transparent and colourless, but it soon becomes 

 more or less opaque on immersion in water or spirit ; in the for- 

 mer it swells if flaccid previously, and in the latter it shrinks by 

 exosmosis. 



The walls of the cyst are composed of numerous very delicate la- 

 minae, of a diaphanous substance, which, in the opaque state, and 

 under a high power, exhibit a very minutely granular aspect. All the 

 lamina) are of extreme fineness, but the inner ones appear to be thin - 

 ner and more readily detached than the more external ones, and the 

 innermost of all is uneven and granular on the surface, and has adhe- 

 rent to it, in the natural and undisturbed state, the bunches or small 

 masses of Echinococci ; or rather these masses appear to be attached 

 to the next layer to the innermost, which is prolonged over and enve- 

 lops them. This may be better understood by inspection of the sub- 

 joined diagram. 



Small opaque masses are seen here and there disseminated in 

 the substance of the walls. The walls of the cyst are very elastic, 

 and when a puncture is made in them the fluid is ejected with con- 

 siderable force, and at the same time the internal membrane is usually 

 detached, together with the adherent vermiculi, aud both are either 

 expelled with the fluid or fall together to the bottom, forming a gluti- 

 nous membraniform mass, in which it is sometimes difficult to find 

 the Echinococci. All the cysts contain vermiculi, and the latter are 

 probably not always more numerous in proportion to the size of the 

 cyst. 



The fluid contained in the cyst is limpid and colourless, and when 



