262 TUBERCULOSIS 



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 /x in thickness, i.e. in proportion to their length 

 they are comparatively thin organisms (Figs. 77 and 78). Some- 

 times, however, longer 

 forms, up to 5 /x or more 

 in length, are met with, 

 both in cultures and in 

 the tissues. They are 

 straight or slightly curved, 

 and are of uniform thick- 

 ness, or may show slight 

 swelling at their extremi- 

 ties; When stained they 

 appear uniformly colour- 

 ed, or may present small 

 uncoloured spots along 

 their course, with darkly 

 stained parts between. In 



such a minute organism 

 FIG. It. Tubercle bacilli, from a pure ... -, J-&, u 



culture on glycerin agar. ^ 1S extremely difficult 



Stained with carbol-fuchsin. x 1000. to determine the exact 



nature of the unstained 



points. Accordingly, 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 consider 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 stain- 

 ing is met with ; this latter condition is, however, not found to 

 be 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 



