320 BOVINE PATHOLOGY. 



vessels, and from the latter into the bronchial tubes. 

 The arguments which have been brought to support 

 this, the most probable, view are that this is undoubtedly 

 the method of distribution of many forms of parasites, 

 and the disease is most frequent and the worm in the 

 lungs are most numerous in young animals in which the 

 tissues are most readily permeable. Other views are 

 those of direct migration from the alimentary canal and 

 entry through the larynx. There is no evidence to sup- 

 port the former view ; the latter is based upon the idea 

 that it is possible for entry to occur even in spite of 

 the coughing, which would result from the passage 

 of the worms through the glottis ; this is rather doubtful. 

 Again, they might, when immature and small, be carried 

 in with the inrush of air during inspiration. This view 

 does not account for the boring armature of the animal, 

 and it has not been found en voyage. As is usual with 

 parasitic affections, this disease is prevalent in wet seasons, 

 on low lands which are liable to flooding. It is seen par- 

 ticularly in calves kept out late in the autumn, and as a 

 result of feeding over land which has been previously 

 pastured by affected animals. It attacks a number of 

 animals at once, and the weakest are the first to give 

 way. The special nature of the irritant determines cer- 

 tain special features in the symptoms. Thus, acute 

 febrile signs are absent, except when the debility causes 

 that form of fever known as hectic. This only is observable 

 in the later stages. The cough is remarkably forcible, 

 distressing, and of a special hacking and paroxysmal 

 character. It leads to the expulsion of stringy mucus, 

 in which parasites may be detected or their ova observed 

 under a low power of the microscope. The attack has a 

 subacute character, and proves very exhausting. Thus, 

 emaciation rapidly increases, and diarrhoea sets in as a 

 complication. The parasites, embedded in stringy mucus, 

 lie intertwined in groups, or stretched against the bron- 

 chial mucous membrane. When in balls they block up 

 the air-passages; they also cause spasm of the bronchial 

 tubes. Thus, they seriously impede respiration, which is 



