662 Gid. 



lutely rare in older animals. The increasing resistance offered 

 to the disease with advancing- age in all probability is connected 

 with the greater delicacy of the tissues in young animals, this 

 favoring the migrations of the parasites. 



According to tlie older authors ca'iiurus oysts are exceptionally found in 

 lambs at the time of birth or a few days after (Simonds, Hering). If these obser- 

 vations are correct tlie embryos must have entered the body of the fetus by way 

 of the placental blood vessels. 



Pathogenesis. The oncospheres reach the cortex by way 

 of the blood vessels of the pia mater and may penetrate into 

 the medullary substance. During their passage they make 

 tracks, and set up inflammation in the immediate neigiil)orhood. 

 This circumscribed inflammation causes no disturbance of the 

 functions of the brain, provided the inflamed areas are few in 

 number; l)ut where the parasites are numerous, there may be 

 severe disturbances, owing to the larger number of small cen- 

 ters. The development of the embryos into cysts increases the 

 intracranial pressure in proportion to the size of the cysts, this 

 pressure causing atrophy of the nervous tissue in the neighbor- 

 hood and in more remote parts of the brain. As a result of 

 this destruction of nervous tissue, both general and local symp- 

 toms make their appearance. 



Anatomical Changes. In the sheep in the acute stages one 

 can see small tracks in the cortex of the upper portion of the 

 hemispheres corresponding with yellowish purulent streaks in 

 the arachnoid, while the inner surface of the dura may be cov- 

 ered with a purulent layer. One can also see green or greenish- 

 yellow Ijladders containing pus-like material contained within 

 translucent membranes. These vary in size from a pin's head 

 to a linseed and they are surrounded by a layer composed of 

 the remains of destroyed tissue and calcified granules, Avhile 

 there may be small hemorrhages round about. The fluid con- 

 tained in the ventricles may be increased in amount and turbid, 

 especially if, as is exceptionally the case, the small cysts have 

 invaded the venous plexuses. 



In the chronic stage, as a rule, only one or two and more 

 rarely as many as six cysts may be found. Ilink records a 

 case in which there were 17 and Huzard even 30. Sometimes 

 small granules, the remains of dead embryos, can be recognized 

 in the membranes. The larger cysts are generally found on 

 the convex surface of the brain or in the hemisphere, but they 

 may be occasionally found in connection with the cerebellum, 

 or the base of the brain. Their connection with the pia mater 

 is generally easily discovered. The brain tissue appears atro- 

 phied and anemic, and in the immediate neighborhood of the 

 cysts is converted into a reddish granular mass, or in some 

 cases it may have a viscid consistency. In the great majority 

 of cases one, and more rarely both, the hemispheres are de- 



