ETIOLOGY 235 



perhaps to the fact that the sheep are slaughtered before the 

 disease has time to develop. It does not occur in epizootic 

 form although it is more prevalent in certain localities than in 

 others. 



§ 166. History. The name "ovine caseous lymph 

 adenitis" was proposed by Norgaard and Mohler iu 1899. 

 These writers found the lesions and the accompanying micro- 

 organism to correspond with those described by Preisz and 

 Guinard in 1891 as pseudo- tuberculosis. The bacterium was 

 fully described by Preisz in 1894. The organism has been 

 found and identified from a large variety of lesions in a number 

 of species of animals. It appears that at least many of the 

 cases of lymphatic gland enlargement in sheep heretofore called 

 pseudo-tuberculosis belong to this disease. Gilruth prefers the 

 name pseudo- tuberculosis. Cherry and Bull describe it as 

 caseous lymphatic glands and Sivori as caseous broncho-pneu- 

 monia, the bacterium of Preisz being found as the probable 

 cause in each case. 



§ 167. Geographical distribution. In the United 

 States this disease is quite common in certain districts in the 

 western and southwestern states. It exists in South America, 

 New Zealand, Australia and Europe. 



Sivori found that 10 per cent of the old sheep killed in 

 Buenos Ayres were affected. The prevalence of the disease in 

 the United States is indicated by the reports of the federal 

 meat inspectors, which show that of 16,000,000 sheep slaugh- 

 tered in Chicago, Kansas City and South Omaha 3,236 were 

 condemned for caseous lymph-adenitis or lesions which might 

 be confounded with it. It is reported by an inspector from Los 

 Angeles that of 950 sheep coming from a certain district, 82 

 were suffering from lymph-adenitis. 



§ 168. Etiology. Caseous lymph-adenitis is caused by 

 a specific microorganism first described by Preisz as the 

 bacillus of pseudo- tuberculosis. Its description shows it to 

 vary in size to such a degree that its polymorphism is said to 

 be characteristic. It is non-motile and hence belongs to the 



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