AVIAN TUBERCULOSIS. — SYMPTOMS AND PATHOLOGICAL ANATOMV. 529 



minations carried out principally on the liver, an organ which readily 

 lends itself to a study of this character. 



In the pheasant the smallest tubercles are formed by a central mass 

 of epithelioid cells surrounded by round cells. 



In the largest tubercles the centre displays a cavity containing 

 epithelioid cells, either crowded together in large numbers, or few and 

 separate. This cavity, being more or less rounded and usually sharply 

 delimited by a layer of dense connective tissue, might be mistaken for 

 a vessel unless care were taken to examine a series of preparations. It 

 is surrounded by layers of epithelioid cells. The latter are separated 

 from one another by connective tissue attached to that surrounding 

 the central cavity. Finally, the periphery of the tubercles is often 

 surrounded by a layer of round cells. 



The largest tubercles show two well-defined zones, a central and 

 a peripheral. The internal is chiefly formed by a compact or vacuo- 

 lated connective tissue, the cells of which, however, display no nuclei 

 capable of being stained. Here, again, we find the pseudo-vascular 

 cavity, which only contains shapeless cellular debris and granulations. 

 The peripheral zone is composed of masses of epithelioid cells separated 

 by connective tissue, and is surrounded by round cells. 



Such is the structure of the simple tubercles. At many points 

 these approach, touch, or become mutually fused together, so much 

 so that in the internal zone of the largest tubercles, for example, one 

 generally finds several cavities resembling blood-vessels. 



The epithelioid cells which enter into the formation of the tubercles 

 are generally provided with a single nucleus ; a certain number, how- 

 ever, possess several, and some, of enormous size and principally 

 situated in the centre of the tubercles, are half surrounded, or even 

 completely surrounded, bj^ nuclei, forming true giant-cells. 



The connective tissue of the tubercles is coloured brownish red by 

 a watery solution of iodine, and rose-red by methyl violet, thus resem- 

 bling amyloid material. 



The bacilli in the tubercles stain readily by Ehrlich's or Herman's 

 methods. They are either isolated, or, as has been well figured by 

 MM. Cornil and Megnin, collected in more or less rounded clumps, 

 surrounded by epithelioid cells. Though numerous in the epithelioid 

 " nests," of which the smallest tubercles consist, they are even more 

 common in tubercles of medium size, particularly in their pseudo- 

 vascular spaces, where they often form compact masses. They par- 

 tially or entirely disappear in the internal zone of the largest tubercles. 



The hepatic tissue between the tubercles shows no alteration, and 



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