160 HYDATIDS AND ECHINOCOCCI. 



magnitude, and their number not unfrequently amounts to 

 several hundreds, or even thousands. Pemberton counted 

 560 hydatids in one cyst, and Allen 7,000 to 8,000- 

 The larger vesicles sometimes contain smaller ones of a 

 third generation, and occasionally the latter in their turn 

 contain others of a fourth generation. From this remark- 

 able development and increase in numbers, it can readily 

 be understood how the size of the mother-sac must in- 

 crease, according to the number and size of the daughter 

 and granddaughter vesicles, and in proportion to the 

 quantity of contained fluid, which often attains to the 

 side of a man's head, and even much larger. This growth 

 of the mother-sac may go on until it ruptures, and then 

 only a few shreds of it may be found lying among the 

 daughter and granddaughter cells. In their unim- 

 paired vegetation, however, these vesicles are filled to 

 repletion, are distended and elastic, and impart to pal- 

 pation a sense of tremulous fluctuation the "hydatid 

 tremulousness " of Kokitanski. 



2. Echinococcus. On a close inspection of the inner 

 surface of these vesicles, we perceive in mauy of 

 them a whitish, opaque, gritty efflorescence, usually 

 aggregated in groups ; and if submitted to the field 

 of the microscope there is revealed to our anxious 

 gaze thousands of densely nestled animalcules, which 

 prove by the most varied changes of form that they 

 long continue to live on in the dead subject. Many of 

 them are likewise found free in the liquid found in 

 these vesicles. These are the scoloces the embryo, in 

 fact, of the " Taenia echinococcus," in various gradations 

 of development. This entozoon is from the ^ to the of 

 a line in length ; its head is similar to that of the teenia ; 



