15 



the cyst has not been disturbed and is quite recent, it exhibits under 

 the microscope only the Echinococci, and occasionally some irregular 

 granular masses. 



The Echinococcus. — When a large hydatid cyst, for instance, in 

 the liver of a sheep, very shortly after the death of the animal, is care- 

 fully opened, at first by a small puncture, so as to prevent the too 

 sudden exit of the fluid and collapse of the cyst, its internal surface 

 will be found covered with minute, opaque granulations resembling 

 grains of sand. These bodies are not uniformly distributed all over 

 the cyst, but are more thickly situated in some parts than in others. 

 They are detached with the greatest facility and on the slightest mo- 

 tion of the cyst, and are rarely found adherent after a few days' delay. 

 When detached, they subside rapidly in the fluid, and consequently 

 they will then usually be found collected in the lowest part of the 

 cyst and frequently entangled in fragments of its innermost thin mem- 

 brane. When some of these granulations are placed between glass, 

 under the microscope, each will be found to be composed of numerous 

 individual Echinococci, more or less closely packed together, and en- 

 veloped almost entirely in a delicate membrane, PL 1. fig. 1. Upon 

 farther pressure being employed, it will be seen, after the rupture of the 

 enveloping membrane, that the Echinococci composing the granula- 

 tions are all attached to a common central mass by short pedicles, 

 which, as well as the central mass, appear to be composed of a 

 substance more coarsely granular, by far, than that of which the 

 lamina? of the cyst are formed (fig. 2). This granular matter is pro- 

 longed beyond the mass of Echinococci into a short pedicle, common 

 to the whole, and by which the granulation is attached to the interior 

 of the hydatid cyst as above described. 



Fig. 2 also shows the mode of interunion of the Echinococci, and the 

 fusion of their separate pedicels into a central mass of granular mat- 

 ter; and it is particularly to this point in the description of the Echino- 

 cocci that I wish to call your attention, and to assure you of its reality, 

 for it is one of those facts, which, though noticed by the earlier wri- 

 ters on the subject, has never been clearly described or figured, and 

 any adhesion between the Echinococci and the cyst has been repeat- 

 edly denied by some of the first authorities on the subject, and par- 

 tiularly by M. Livois, whose monograph shows the great pains and 

 attention he has devoted to this subject, and whose observations and 

 descriptions in other respects so minutely correspond with those I 

 have been able to make. 



The Echinococcus occurs in two forms, viz., with the head 



