398 Veterinary Medicine. 



which may become inspissated so as to resemble rich, old, ripe 

 cheese, and finally a dry, floury powder. These caseous contents 

 are remarkable for their yellowish green color, which recalls the 

 intestinal nodules caused by the CEsophagostoma Columbiana. 

 The capsule forms a smooth, clearly defined limitation membrane, 

 separating the mass from the surrounding healthy tissues. When 

 caseation has taken place there is no external zone of congestion 

 nor inflammation as in tuberculosis or glanders. 



In the early nodules before caseation, the tissue is seen to con- 

 sist mainly of leucocytes and nucleated cells, round, or of an ir- 

 regular outline and granular. In the centre of the nodule the 

 cells are already breaking up and disintegrating into a granular 

 debris. The bacteria, oval, dumb-bell or club-shaped, are found 

 among and even within the leucocytes and mingled with the 

 debris. 



The miliary nodule in the liver of an inoculated animal, killed 

 after three weeks, is thus described by Norgaard and Mohler : — 

 ' ' A caseous centre composed of an amorphous material which 

 does not take any of the ordinary stains. Surrounding the centre 

 may be seen numerous leucocytes, more or less degenerated and 

 frequently containing one or more bacilli, while clumps of these 

 organisms are scattered among them. External to this is a 

 dense round-cell infiltration, the peripheral zone of which is 

 undergoing connective tissue metamorphosis and serving as a 

 line of demarcation between the atrophied liver cells and the cen- 

 tral cell-mass. This process then repeats itself centrifugally, 

 causing the appearance of concentric layers, until a sufiiciently 

 strong reaction takes place to form a connective tissue barrier 

 strong enough to encapsulate the central part of the nodule and 

 prevent its further growth." 



Before the mass is encapsulated in this way the bacteria easily 

 escape into the lymph channels and are washed on to form the 

 nuclei of new nodules in the lymph glands and even in the 

 lymph plexuses of connective tissue. In this way may be ex- 

 plained much of the work of generalization in which multiple 

 nodules and centres of caseation are found in the lungs, bron- 

 chial walls, liver, spleen, kidneys and other parts. 



Differential diagnosis. From phlegmonous abscesses this is to 

 be distinguished by its slow progress, by the absence of acute 



