56 JOHNE^S DISEASE 



and chloroform or xylol, and at the end of an hour 

 transfer to pure paraffin for two hours, the paraffin 

 being changed once. The tissue should then be set in 

 blocks of paraffin, in the ordinary way, by means of 

 two L blocks. 



The sections should be cut as thin as possible — 

 about 4 fjb — a good microtome, such as a Cambridge 

 rocker, being necessary for this purpose. It is best 

 to cut the bowel in a transverse direction at right 

 angles to the surface, in order to obtain a clear view 

 of the villi and their relation to the deeper tissues. 

 Sections, after being treated with xylol and absolute 

 alcohol, are stained by Gram's method, or, better, with 

 carbol-fuchsin and a contrast stain such as methylene 

 blue (Ziehl-Neelsen's method). If stained by the 

 latter method the bacilli are coloured a bright red, 

 in contrast to the tissues, which are coloured blue. 

 Histological changes can be observed better if the 

 sections are stained with haematoxylin and eosin. 



We have seen that on post-mortem examination the 

 macroscopical appearances of the gut which are 

 especially characteristic are the general thickening 

 of the organ and the great prominence of the corruga- 

 tions. There is no caseation, and no sign of any 

 ulceration or fibrosis of the tissues, and although in 

 some cases vascular congestion may denote a certain 

 amount of inflammation, this is by no means always 

 present. Thus the post-mortem appearances of the 

 gut lead one to assume that Johne's bacillus does not 

 give rise under natural conditions to an acute in- 

 flammation, and microscopical examinations of both 

 early and advanced cases confirm this view. 



As we have seen, the alimentary tract may be 

 affected from the duodenum to the margins of the 

 anus, and Johne's bacillus may be found within these 



