590 DISEASES OF CATTLE, SHEEP, GOATS, ETC. 



upon the blood. This worm is rarely found in large numbers, other- 

 wise it might become a serious parasite. It probably causes more 

 losses now than are attributed to it. 



Hair Lung Worm (Strongylus Ovis Pulmonalis). The hair 

 lung worm is the smaller of the two varieties of worms affecting the 

 lungs. It is the one that inhabits the smaller air cells and the dis- 

 ease caused by it is a pneumonia, as distinguished from the large 

 lung worm affecting the bronchi and causing bronchitis or hacking 

 cough. 



This lung worm is so small that it escapes the attention of the 

 flock master, and farmer. What he finds upon post-mortem is solidi- 

 fied lung as in pneumonia. The disease is generally referred to as 

 pneumonia, and it is only when a competent observer is employed 

 or that the history of a number of cases is presented, do we get a 

 diagnosis of the parasitic character. The disease is of much more 

 frequent occurrence than is at all suspected. 



The complete life history of the worm remains to be determined. 

 The young escape from the lungs during acts of coughing, but what 

 becomes of them from that time until they are again found in the 

 lung has not been determined. It is surmised that they undergo 

 such changes as may be necessary on the pasture or in water and 

 after a short time are again taken into another animal while graz- 

 ing or with the drink. Whether they find an intermediate host in 

 some insect or low form of animal life is not known. Some ob- 

 servers reasoning from analogy consider that such is a part of the 

 life cycle. Other observers do not consider such to be a necessary 

 part of the life cycle. The disease is only on certain pastures pas- 

 tures that have become infected through bringing in some diseased 

 sheep. The disease spreads throughout a flock to greater extent on 

 very wet years than in years of drought. A fairly low pasture used 

 continuously throughout the season is also bad. Its ill effects are 

 most marked upon old sheep. 



This parasite penetrates the air passages to its most minute 

 branching. It causes irritation and inflammation of the wall of the 

 air passage and cells and a general -breaking down of the tissue. As 

 in all inflammatory processes nature attempts its arrest of extension 

 by walling it off. Each worm then becomes the center of a slight in- 

 flammatory area that is walled off and resembles a tubercle. The 

 contents of the inside are broken down and galatinous, outside the 

 capsule is firm and fibrous. These tubercles are about a twentieth 

 of an inch in diameter at first, but in the later stages becomes about 

 an eighth of an inch in diameter. The parasite is always found 

 in the central part surrounded by greenish or yellowish material, 

 thin and pus-like, or may be dry and cheesy. They may become 

 calcareous by lime deposition. These tubercles undergo quite a se- 

 ries of changes from that of a simple blood spot under the pleura to 

 that of a hard grey nodule. When the worm matures it migrates 

 to the bronchia to mate and lay eggs, and these hatch and the young 

 being very active set up an inflammation. If it is severe we have 

 the pneumonia that sickens or kills the sheep. The pneumonic 



