DISEASES OF THE OX AND SHEEP. 449 



importance on account of the large number of lambs which it 

 attacks. It is particularly prevalent in jthe latter part of 

 summer and the early part of autumn in low-lying damp 

 localities, although it is by no means confined to them, being, 

 for instance, very common on the Wolds of North Lincolnshire. 

 The length of the male Strongylus Jilariay the worm which 

 causes the malady, is about If inch, while that of the female is 

 somewhat in excess of this. In older sheep the worms are 

 generally found encased in the tissue of the lungs, whereas 

 in lambs they are generally present in the air-tubes. 



The lungs of sheep which have been infested with these 

 parasites contain large numbers of little rounded masses, some 

 hollow and containing fluid, others containing semi-fluid matter, 

 while others again are very hard and calcareous. The different 

 characters of these little nodules, which vary in size from that 

 of a mustard seed to that of a lentil seed, represent different 

 stages in their growth. Each nodule contains tiny worms 

 lying coiled up within. These little masses do not of necessity 

 cause very much mischief, though they may bring on great 

 weakness and death. 



If the carcase of a lamb which has died of verminous bron- 

 chitis be examined, the wind-pipe and the air-tubes will be found 

 to be more or less choked up with worms. Mr. Crisp believes 

 that the worms pass in the first instance into the stomach, and 

 then, by the regurgitation of the food which precedes the chewing 

 of the cud, make their way into the breathing organs. Another 

 view is that the eggs of the parasite are taken into the stomach 

 together with the food. From the stomach the young parasites 

 gain access into the circulation, and thus make their way into 

 the lungs. 



Those who hold that the lambs take in the eggs of worms 

 discharged by the older sheep readily explain the fact that a 

 whole flock may become infected by the ova and parasites 

 expelled by even apparently healthy animals ; for, as we have 

 above pointed out, sheep do not by any means invariably mani- 

 fest symptoms of the presence of these uninvited guests. The 

 view entertained by the late Professor Cobbold is probably 

 correct, namely, that the parasite passes one stage of its 

 existence in the body of the earthworm or of some mollusc, 

 which discharges the immature parasites upon the grass. While 



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