187 



young worm must escape from the sheep in order to spend a portion of 

 its life on the ground or in some of the minute forms of animals before 

 they are capable of further development in the sheep. Most authors 

 are agreed that the worm passes into the lungs by the trachea either 

 during feeding or rumination. The length of time which it takes the 

 worm to complete its cycle of life is yet unknown. As the most pro- 

 nounced cases among slaughtered animals are in the older sheep, it would 

 seem as though this parasite was of very slow growth, requiring years 

 instead of months for successive generations to produce a disease fatal 

 to the infested sheep. It may be, however, that many lambs and 

 young sheep are so seriously affected with the parasite that they either 

 ilie or become so inferior in quality that they are never taken to the 

 abattoir. In this case the cycle of life would x^^ove to be rapid. 



Disease. — The diagnosis of verminous pneumonia in living animals 

 is a difficult matter. Not until the disease is so far advanced that its 

 cure is hopeless are any well-pronounced symptoms developed. The 

 worst affected sheep may have a deep cough, be out of condition, and 

 be generally ana?mic, as shown by the pallor of the visible mucous mem- 

 brane and the dry, harsh coat. They are likely to lose flesh, but some, 

 if not seriously affected, fatten tolerably well. 



The^os;^ mortem diagnosis is as certain and definite as the diagnosis 

 in life is unsatisfactory. So pronounced are the lesions caused by the 

 worms in the lung tissue that any one having once seen a diseased 

 lung would easily recognize it again. The little tubercles, filled with 

 greenish material and surrounded by more or less of the thickened 

 lung tissue which when cut exudes a frothy liquid, are diagnostic. 

 The presence of the worm in these tubercles is decisive. 



The prognosis of this disease can not be definitely given. From many 

 examinations of affected lungs it seems to me that the disease is a pro- 

 gressive one, producing its worst effects as the sheep grow old. Where 

 the sheep are marketed young the loss from this parasite is compara- 

 tively small ; but where the disease is wide-spread and affects whole 

 flocks, though but a few cents may be lost per head, the aggregate loss 

 to the sheep industry must be considerable. To this must be added the 

 loss from the disease in its more severe stages. When the disease is 

 once in a flock and the farm or range is infected with it there will be a 

 steady loss resulting until the disease is in some way exterminated. 



Pathology. — The disease created is dependent upon the life history of 

 thp parasite as to character and upon the numbers of the invading hosts 

 for its intensity. The changes produced in the lungs are but the aggre- 

 gate of all the changes which result from the different invading individ- 

 uals, and the history of the changes wrought by a single parasite illus- 

 trates the changes produced by all. The minute worm, when entering, 

 penetratesthe air passages to their extremities. In the ultimate alveoli 

 it breaks down some portion of the membranous partition and becomes 

 surrounded by the products of the inflammation which it excites and 



