346 Tuberculosis 



Morphologic Peculiarities. Morphologically, the or- 

 ganisms found in avian tuberculosis is similar to that found 

 in the mammalian disease, but is a little longer and more 

 slender, with more marked tendency to club and branched 

 forms. Fragmented and beaded forms occur as in the 

 human tubercle bacilli. 



Staining. The avian bacillus stains in about the same 

 manner as the human and bovine bacilli and has an equal 

 resistance to the decolorant effect of acids. 



Cultivation. Marked rapidity and luxuriance of growth 

 are characteristic of the avian bacillus, which grows upon 

 agar-agar and ordinary bouillon prepared without glycerin. 



The growth also lacks the dry quality characteristic of 

 cultures of the human and bovine bacilli. Old cultures of 

 the bacillus of fowl tuberculosis turn slightly yellow. 



Thermic Sensitivity. The bacillus also differs in its 

 thermic sensitivity and will grow at 42-45 C. quite as 

 well as at 37 C., while the growth of the human and mam- 

 malian bacilli ceases at 42 C. Moreover, growth at 43 

 C. does not attenuate its virulence. The thermal death- 

 point is 70 C. Upon culture media it is said to retain its 

 virulence as long as two years. 



Pathogenesis. Birds are the most susceptible animals 

 for experimental inoculation, the embryos and young being 

 more susceptible than the adults; guinea-pigs are quite 

 immune, or after inoculation develop cheesy nodes, but do 

 not die. Artificial inoculation can be made in the subcu- 

 taneous tissue, in the trachea, and in the veins; never 

 through the intestine. After inoculation the birds die in 

 from one to seven months. The chief seat of the disease 

 is the liver, where cellular (lymphocytic) nodes, lacking the 

 central coagulation and the giant-cell formation of mam- 

 malian tuberculosis, and enormously rich in bacilli, are 

 found. The disease never begins in the lungs, and the 

 fowls that are diseased never show bacilli in the sputum or 

 in the dung. 



Rabbits are easily infected, an abscess forming at the 

 seat of inoculation, nodules forming later in the lungs, so 

 that the distribution is quite different from that seen in 

 birds. It is probable that the avian bacillus occasionally 

 infects man. 



The possibility that this bacillus is derived from the same 

 stock as the tubercle bacillus is strengthened by the experi- 



