1 66 OVINE CASEOUS LYMPH-ADENITIS 



tissue metamorphosis and become organized into an encap- 

 sulating membrane. 



When a miliary nodule from the liver of an experimental 

 animal which has been destroyed three weeks after inoculation 

 is examined microscopicalh^ the following picture is observed. 

 A caseous center composed of an amorphous material that 

 does not take any of the ordinar}' stains. Surrounding the 

 center ma}- be seen numerous leucocytes more or less degener- 

 ated and frequently containing one or more bacteria while 

 clumps of these organisms are scattered among them. Ex- 

 ternal to this is a dense round cell infiltration the peripheral 

 zone of which is undergoing connective tissue formation thus 

 serving as a line of demarcation between the atrophied liver 

 cells and the central cell ma.ss. The process then repeats itself 

 until a connective tissue barrier strong enough to encapsulate 

 the central part of the nodule and prevent its further growth 

 is obtained. The nodules in the kidneys and lungs present a 

 similar microscopic appearance, excepting that the foci in the 

 lungs are more regular on account of the catarrhal inflamma- 

 tion that accompanies the reaction of the surrounding tissue. 

 The center contains a dense mass of disintegrated cell structures 

 composed of the desquamated and proliferated epithelial cells, 

 degenerated leucocytes and round cells. In experimental 

 animals which succumb quickly to an intravenous injection of 

 virulent material, the lung tissue immediately surrounding the 

 nodules is frequently seen to be hepatized. 



§ 125. Differential diagnosis. This specific lymphatic 

 affection is to be differentiated from, (i) other infections which 

 may cause enlargement or suppuration of lymph glands, and 

 (2) tuberculosis. If the diagnosis cannot be made from the 

 gross appearance of the lesions a bacteriological examination 

 will be necessar}'. The fact should be kept in mind that 

 tuberculosis in sheep is ver}- rare. With lymph-adenitis, 

 cultures in ordinary media will give a growth of the bacterium 

 of Preisz. With tuberculosis the result would be negative. 

 (See tuberculosis) It is important not to confuse the nodular 

 disease of sheep's intestines with this affection. The location 



