CA USES OF DISEASE. 2 1 9 



which has died of this disease we find the liver and 

 intestines presenting numerous rounded nodules of a 

 pale yellow colour, varying in size from a pin point to 

 that of a filbert. On cutting into the larger nodules the 

 centre is found occupied by pus. The smaller ones are 

 homogeneous, and on examining them microscopically 

 we recognize in the centre small circular cells with larger 

 ones giant-cells lodged among them, outside these a 

 layer of smaller cells with no giant-cells, and lastly a 

 layer of fibrous tissue. 



When such specimens are suitably stained, minute 

 rod-like bodies bacilli are 

 seen clustered in the centre 

 of the mass and occupying 

 the interior of the cells, espe- 

 cially the giant-cells. In 

 nodules of moderate size the 



Centre is Occupied by CaseOUS FIG. 115. Leucocytes ingesting 



material surrounded by a zone 



of cells containing bacilli. Adjacent nodules may 

 coalesce and thus produce large masses. The blood-vessels 

 connected with the nodules frequently present clusters 

 of bacilli in their interior. An extensive and prolonged 

 study of this disease has convinced me that the bacilli, 

 from whatever source arising, are introduced into the 

 alimentary canal and find their way into the walls of the 

 bowel. Here they are attacked by the leucocytes which 

 surround, ingest, and destroy them. The bacilli may be 

 too numerous for the leucocytes, and the point where 

 the bacilli gain entrance into the tissues become a 

 battle-field, large numbers of leucocytes are quickly on 



