468 



NERVOUS SYSTEM. 



varying between that of a pin's head and that of a lentil or a small 

 hazel-nut. 



Later the tracts, with their caseons contents, disapi^ear, and the 

 development of many of the vesicles proves abortive. At the end of 

 a month the vesicles, continuing to develoj) regularly, attain to about 

 the size of a pea. Between the fiftieth and sixtieth days heads or 

 scolices appear in the interior of the vesicle, which then reaches the 



Fig. '21 1. — Brain of sheep. Ccenurosis of the left hemisphere, 

 ffistrus larvse exposed by trepanation. 



dimensions of a hazel-nut. From this time the vesicles continue to 

 increase in size until the death of the patient. Usually they become as 

 large as a walnut, or even larger, and the interior contains hundreds 

 of scolices, each showing a head. 



The cystic phase only develops completely in animals whose brains 

 contain a limited number of cysts, and in such the signs of turn-sick 

 are well developed. In others, where the numbers are large (ten to 

 fifteen embryos or more), death occurs during the primary stage, usually 

 towards the end of the first month, in consequence of acute encepha- 

 litis and without any of the symptoms of turn-sick. 



The number of animals attacked is sometimes enormous. Moussu 



