530 CLINICAL VETERINARY MEDICINE AND SURGERY 



in particular presents neither fatty nor amyloid degeneration, nodular 

 hepatitis, nor cirrhosis. 



The preceding histological details would appear to suggest that in 

 the pheasant the development and subsequent course of hepatic tuber- 

 culosis is somewhat as follows. A colony of tuberculous bacilli first 

 becomes arrested at some point in the liver, where the bacilli multiply 

 and cause a local reaction, indicated by the production of a nest of 

 epithelioid cells. Around this nest round cells group themselves, and 

 a limiting connective-tissue membrane forms, which on section re- 

 sembles the wall of a blood-vessel. This barrier is insufficient to 

 prevent the spread of the tuberculous process. The bacilli pass it, 

 extend beyond, multiply, and cause the development of fresh nests of 

 epithelioid cells, which become surrounded by fresh fibrous limiting 

 membranes. The bacilli thus gradually progress, exciting an epi- 

 thelioid reaction and further formation of fibrous tissue, which, as we 

 have seen, undergoes amyloid degeneration. When the tubercles 

 attain a certain size the connective tissue in the central parts becomes 

 thickened, the epithelioid cells undergo degeneration, and the bacilli 

 cease to stain, but their periphery presents an active zone extremely 

 rich in bacilli and epithelioid cells, the further growth of which only 

 ceases with the death of the animal. 



In the fowl the smallest tubercles are formed of a mass of epi- 

 thelioid cells, surrounded by others of a spherical and fusiform outline. 

 The larger show a central necrotic, hyaline portion coloured brown by 

 picro-carmine. Around this hyaline centre is arranged a border of epi- 

 thelioid cells, usually of considerable size, and always containing a 

 large number of nuclei, which stain vividly with carmine. These cells 

 are generally elongated, and more or less cylindrical in shape, and are 

 arranged perpendicularly to the hyaline zone ; they contain nuclei 

 principally collected at that extremity of the cell farthest from the 

 hyaline zone. It might thus seem at first sight as though the hyaline 

 mass were contained within a bile-duct, in the same way that a super- 

 ficial examination might suggest the existence of vascular cavities at 

 the centre of the tubercles in the pheasant. Outside the border formed 

 around the hyaline zone by the above-mentioned epithelioid cells are 

 masses of ordinary epithelioid cells. The extreme periphery of the 

 tubercle is indicated by round and fusiform cells. 



Certain tubercles of similar size to the preceding are simply formed 

 by masses of epithelioid cells, without the hyaline zone and border of 

 epithelioid cells which distinguish the former. In other tubercles, on 

 the contrary, the central epithelioid mass shows a hyaline zone and a 



