PATHOLOGICAL HISTOLOGY 57 



limits. Sections of badly-affected bowel, stained with 

 carbol-fuchsin, decolorized with 25 per cent, sulphuric 

 acid, and counter-stained with methylene blue, may 

 contain so large a number of bacilli that the section 

 presents a magenta colour to the naked eye. As a rule 

 the number of bacilli present varies directly with the 

 amount of pathological change seen microscopically, 

 and thus they are usually most numerous in and 

 around the ileo-caecal valve, and it is in this situation 

 that the most marked histological changes are found. 



In the small intestines the villi are seen to be swollen 

 and to have a club-shaped appearance, while many of 

 them are flattened on the surface and are stunted. 

 They often contain a large number of clumps of bacilli, 

 mostly at the apex and base, while there is a cellular 

 reaction consisting of epithelioid and round cells and a 

 few giant cells. The bacilli are usually most numerous 

 between the glands and in the lymphoid tissue forming 

 the solitary follicles, but in advanced cases the sub- 

 mucous tissue may be extensively invaded ; the bacilli 

 are, for the greater part, in dense clumps, and are both 

 intracellular and extracellular, while they are some- 

 times found in the characteristic wreath formations. 

 We have not often met with this wreath-like forma- 

 tion of the bacilli, and consider that it is less frequent 

 than is generally supposed. The bacilli seem to spare 

 the gland cells for a long time, as even in advanced 

 cases many of the glands appear to be fairly normal, 

 containing, perhaps, an isolated cell here and there full 

 of bacilli ; however, the glands may be atrophied to a 

 certain extent, presumably by the mechanical effect 

 of the hyperplasia of the adjacent connective tissue. 

 Between the glands, and deep down in the solitar}^ 

 follicles, there are usually a large number of epithelioid 

 and lymphatic cells and a few giant cells. The last- 



