THE NERVOUS SYSTEM 351 



is passed out of the bowel along with the faeces. The segment 

 contains a large number of eggs, and is supposed to be taken up and 

 swallowed along with the herbage on which the animal feeds. On 

 reaching the stomach, the heat therein soon sets the young embryo 

 at liberty, and it is then taken into the circulation and carried by the 

 blood-stream to the brain, which, being its natural habitat, is pre- 

 ferred to any other part of the body, and therefore selected for its 

 abode and further transformation. Here, by its hooked processes, 

 it finds its way through the walls of the vessels into the substance of 

 the brain, and there the cyst, or hydatid, is formed (Plate XIX,, 

 Fig. f.). Should the brain of a sheep or calf- containing this cyst be 

 given to a dog, tape-worms of this particular kind will again be 

 reproduced, and so the cycle of life is carried on. Sheep are more 

 subject to this affliction than any other animal ; but I have seen a 

 number of young stirks, aged from twelve to eighteen months, 

 affected, and of these several recovered after being operated upon. 



574. Symptoms. — The first symptom noticeable is an unsteady 

 gait and a gradual loss of flesh by the animal, which carries the 

 head on one side and walks in a circular direction ; or it may hold 

 the head upwards and backwards, and walk with high-stepping, 

 jerky action. This variation in the symptoms depends upon the 

 part of the brain affected : if on the right side of that organ, the 

 animal will circle to the left, and vice versa; while, if in the middle, 

 the animal steps high and jerky. 



575. Treatment. — Many farmers and shepherds are expert 

 operators for the removal of the cyst. The old method of operation 

 was to determine the position of the cyst by feeling for a softening of 

 the bone. The wool was then clipped off, and the part burnt through 

 with a red-hot poker ; a goose-quill was next inserted, and by its 

 means the fluid and hydatid sac were removed. A plaster of tar or 

 pitch was next placed over the part and completed the operation. 

 The new form of procedure is to open the parts by means of a fine 

 trocar and canula and to draw off the fluid with the aid of a syringe, 

 the sac being next removed by a pair of forceps. Success in these 

 operations greatly depends on the locality of the tumour. 



