DIFFERENTIAL DIAGNOSIS 359 



in number so that the circulation from the inner cells is cut 

 off and they die. Their degeneration gives rise to the cheesy 

 mass. If the worm remained in the center of the mass the 

 new growth would eventually cease, but the worm makes its 

 way to the out.side and at that point keeps up the irritation 

 and new growth. This is shown by and accounts for the dried 

 older parts of the larger nodules and the fresh yellowish-green 

 adjoining parts. As soon as the worm escapes, the irritation 

 ceases, the tumor shrinks and absorption of the mass begins. 

 The irritation produced by the worm provides it with food and 

 favorable surroundings for development. Often the worm 

 dies from weakness or other cau.se and leaves behind those 

 little hard incompletely-grown nodules which have been men- 

 tioned. 



The disease is an insidious one, for not only is the rate of 

 infection gradual, increasing slowly in amount from week to 

 week, but the rate of development of the nodules is very slow, 

 apparently requiring months. It is only w^hen the disease is 

 well advanced that its cumulative effects can be noticed. 



^ 282. Differential diagnosis. The diagnosis of this 

 parasitic disease can only be made from a post-mortem exami- 

 nation. In the living sheep there may be .signs of general 

 debility, bloodless lips and eyes, thin sides and flanks and dry 

 wool. It may be that the flock is not in good condition ; and 

 in severe cases the diarrhoea and emaciation may be excessive. 



The only disease with which this can be readily confused 

 is tuberculosis, which is very rare in sheep. A careful exami- 

 nation of the lesions will reveal the presence of the nematode 

 which will decide the diagnosis. The fact that the lesions are 

 usually restricted to the intestinal wall and that the nodules 

 are sharply circumscribed from the normal tissue aid in the 

 diagnosis from the gross specimen. It is important that this 

 quite common disease should not be diagnosed as tuberculosis. 



§ 283. Prevention. For this disease there is no remedy 

 ■except the removal and extermination of the adult worms. 

 They are usually buried deeply in the mucous secretions of 

 the intestinal mucosa to which they are attached. They may 

 iDe found in considerable numbers in old sheep. The medi- 



