AVIAN TUBERCULOSIS. — SYMPTOMS AND PATHOLOGICAL ANATOMY. 531 



border of epithelioid cells, distinguished from the others by their 

 direction, form, large size, number, and by the position and staining 

 of their nuclei. In some of these tubercles the hyaline zones tend to 

 become, or do in reality become, fused. 



The largest tubercles, composed of large numbers of epithelioid 

 masses, display a faint indication of a connective-tissue capsule. The 

 hyaline degeneration is then extensive, and replaces the epithelioid cells. 

 Certain of these tubercles resemble old syphilitic gummata, and appear 

 simply formed of an encapsuled hyaline mass. 



In tuberculosis of the fowl the bacilli stain readily by Ehrlich's 

 method. They are contained in very large numbers in the epithelioid 

 cells, and though usually isolated are sometimes collected in clumps, 

 as in tuberculosis of the pheasant. They are also found in the smallest 

 tubercles formed of a simple mass of epithelioid cells. In the larger 

 tubercles they are more numerous, particularly in the vitreous zone, 

 where they appear of great size and with a tendency to branch : the 

 epithelioid border of the hyaline zone, on the contrary, contains ex- 

 tremely few ; under any circumstances it contains much fewer than the 

 epithelioid masses towards the periphery of these tubercles. 



The first stage in the tuberculous process in the liver of the fowl, 

 as in that of the pheasant, is therefore marked by the development, in 

 consequence of microbic irritation, of an epithelioid mass, which is 

 surrounded by spherical and fusiform cells. Around this primary 

 mass of epithelioid cells others successively form. The centre of the 

 primary clump of cells undergoes hyaline degeneration, as does that of 

 the later formations ; necrobiosis tends to replace the tuberculous 

 neoplasis, whilst a fibrous barrier develops around the periphery of the 

 tubercle. The tubercle may thus cease to grow, and become com- 

 pletely transformed into an encysted hyaline mass. But this is excep- 

 tional ; whilst the older portions of the tubercles undergo degeneration 

 bacilli escape through the imperfect fibrous barrier which surrounds 

 them and spread into healthy tissue, in which they produce a crop of 

 fresh tubercles. 



To sum up, although the initial stages of tubercle formation in the 

 liver of the fowl and of the pheasant are identical, later development is 

 marked by notable differences. 



In the pheasant the tubercle bacillus causes development of epi- 

 thelioid cells ; these soon undergo molecular degeneration and are 

 succeeded by formation of abundant connective tissue, which surrounds 

 pseudo-vascular cavities and undergoes amyloid degeneration. 



In the fowl the epithelioid cells undergo hyaline necrobiosis, which, 



