THE TUBERCLE BACILLUS 237 



Tuberculosis in fowls (avian tuberculosis) is a common and very 

 infectious disease, nearly all the birds in a poultry-yard being sometimes 

 affected. 



From these statements it will be seen that the disease in 

 animals presents great variations in character, and may differ in 

 many respects from that met with in the human subject. The 

 relation of the different forms of tuberculosis is discussed below. 



Tubercle Bacillus Microscopical Characters. Tubercle 

 bacilli are minute rods which usually measure 2 '5 to 3 -5 ^ in 

 length, and '3 /A in thickness, i.e. in proportion to their length 

 they are comparatively thin organisms (Figs. 82 and 83). Some- 

 times, however, longer 

 forms, up to 5 /A or more 

 in length, are met with, 

 both in cultures and in the 

 tissues. They are straight * 



or slightly curved, and are 

 of uniform thickness, or 

 may show slight swelling 

 at their extremities. When 

 stained they appear uni- 

 formly coloured, or may 

 present small uncoloured 

 spots along their course, 

 with darkly -stained parts 

 between. In such a min- 

 ute organism it is ex- 

 tremely difficult to deter^ FJG 82 ._Tubercle bacilli, from a pure 

 mine the exact natures. of culture on glycerin agar. 



the unstained points. Ac- Stained with carbol-fuchsin. x 1000. 

 cordingly, we find that 



some observers consider these to be spores, while others find that 

 it is impossible to stain them by any means whatever, and con- 

 sider that they are really of the nature of vacuoles. Against their 

 being spores is also the fact that many occur in one bacillus. 

 Others again hold that some of the condensed and highly-stained 

 particles are spores. It is impossible to speak definitely on the 

 question at present. We can only say that the younger bacilli 

 stain uniformly, and that in the older forms inequality in staining 

 is met with ; this latter condition is, however, not associated with 

 greater powers of resistance. 



The bacilli in the tissues occur scattered irregularly or in 

 little masses. They are usually single, or two are attached end 

 to end and often form in such a case an obtuse angle. True 



