PATHOLOGICAL HISTOLOGY 61 



similar to tuberculosis. The absence of caseation (and 

 consequently of ulceration) is one of the most im- 

 portant differences, and, indeed, cellular degeneration 

 can rarely be recognized, except that the nuclei of the 

 cells may lose to a certain extent their power of stain- 

 ing. The general diffusion of the lesions and the 

 absence of any fibrous -tissue capsule are also dis- 

 tinctive features ; but perhaps the most prominent 

 difference between this disease and tuberculosis is to 

 be found in the number of causal micro-organisms 

 present. Owing to the comparatively slight effect of 

 a large number of Johne's bacilli on the surrounding 

 cells, many authors have contended that in all proba- 

 bility Johne's bacillus does not secrete toxins in the 

 same way as the tubercle bacillus does. For this 

 and several other reasons, which are discussed in 

 Chapter IX., we agree with this view; but at the 

 same time it may be mentioned that in animals that 

 do not suffer naturally from the disease, and in which 

 the bacilli do not appear to be able to multiply, the 

 caseous peritoneal glands are indistinguishable from 

 tubercular glands macroscopically, and only differ 

 microscopically as regards the number of bacilli and 

 a slighter degree of caseation. This question is con- 

 sidered more fully in Chapter IX. 



