192 ENTOZOA FOUND IN MAN. 



Chapter XXVII. 



ENTOZOA DEVELOPED IN THE CENTEAL NEEVOUS 



SYSTEM. 



The invasion of the central nervous system by entozoa 

 is not rare in Man and in herbivorous mammiferse. 

 These entozoa belong exclusively to the three genera 

 of vesicular worms, of which only two, the hydatid 

 and the cysticercus, can be considered to exist in the 

 human subject, no well-authenticated instance having 

 been recorded of the occurrence of the coenurus in 

 Man.i 



The pathological phenomena produced by hydatids 

 and by cysticerci present important distinctions. The 

 indefinite increase in size of the former, and the very 

 considerable bulk to which they attain, must sooner 

 or later give rise to serious, and even mortal, com- 

 plications. The cysticerci, which never become very- 

 large, may continue for a long time almost innocuous. 



These entozoa are situated, sometimes externally, 

 sometimes internally, as regards the encephalon, and 

 they may also be developed at any portion of the 



* Although the coenurus, like the hydatids or the cysticerci, 

 may be contained within a serous cavity, the cyst which encloses 

 it never exists excepting in some part of the encephalon, and the 

 coenurus must consequently be regarded as an entozoon peculiar 

 to the nervous system. It is the only entozoon which is known 

 to have its Jiahitat exclusively in the nervous centres. It is more 

 frequent in the sheep than in any other animal, and it produces 

 in the sheep a very peculiar epileptiform affection, to which 

 the name of " Staggers " is commonly applied in agricultural 

 districts. 



