DISEASES DUE TO INTERNAL PARASITES. 229 



creates a doubt whether such a long period of infection was all 

 due to the same parasites or to renewed generations of them. 



The disease ordinarily lasts from three to six months, but 

 this is very uncertain, affected animals having been known to 

 succumb in a few days after infection, the death in such cases 

 being caused by acute inflammation of the liver, due to the irri- 

 tation caused by the presence of the parasites. Sheep suffering 

 from the rot, owing to their weakened condition, become suscept- 

 ible to other maladies which are liable to cause death, even before 

 the liver disease has had time to run its course. 



post-)VIortCTn. 



Post mortem appearances depend entirely on the stage in 

 ^^'hich the sheep is destroyed. Shortly after infection the thin 

 edge of the small lobe of the liver, termed the quadrate lobe, be- 

 comes a whitish-blue color, which spreads along the upper and 

 lower sides. 



When the disease has run a more protracted course, the 

 flesh is found pale, and in the dependant parts of the body in- 

 filtrated with a yellowish serous fluid. In far advanced cases 

 few parts of the body are found which do not present evidences of 

 disease, the heart is soft and pale, the lungs often being studded 

 with tubercles; in all cases the liver is found extensively affected, 

 generally pale in color and friable or mottled, with hard scirrhous 

 spots with a fluid jelly-like deposit on different parts of its sur- 

 face, particularly so around the bile-ducts. It will also appear 

 puckered in places with cicatricial markings, caused by the re- 

 parative process and contraction of the newly formed tissue. 

 Channels are formed in the substance of the organ under the 

 serous membranes covering it. These are visible to the naked 

 eye. The biliary ducts are irregularly enlarged and thickened, 

 the sacculations frequently being as large as a hickory nut, and 

 on making a transverse section of these they will be found to 



