i8o 



TUBERCULOSIS 



slaughter houses of Kansas Cit)', Omaha, Sioux City and 

 Chicago are practically free from this disease. Tuberculosis 

 exists, however, in many places where beef cattle are raised, as 

 the result of the introduction of affected breeding stock. In 

 many localities, especially where there is an extensive inter- 

 change of animals, a large percentage of the herds are more or 

 less affected. 



§ 141. Etiology. Tuberculosis is caused by a rod- shaped 

 organism known as Bacterium tuberculosis. It was discovered 



by Robert Koch in 1882. Schiil- 

 ler and Toussaint had previously 

 studied growths which seem, from 

 the results of their inoculation ex- 

 periments, to have been this organ- 

 ism. The bacterium of tuberculosis 

 is a slender, rod-shaped organism 

 with rounded ends, from 2 to 5/( in 

 length and from 0.3 to 0.5/^ broad. 

 The rods are straight or slightly 

 curved, and occur singly, in pairs 

 or in small bundles. Frequently 

 they cross one another. They do 

 not produce spores, but vacuoles are often observed and 

 branching forms have been described. 



The bacterium of tuberculosis is readily cultivated on 

 artificial media such as blood serum, glycerinated agar and 

 bouillon after it has been adapted to such artificial conditions.'i^ 

 It is, however, not easy to cultivate it directly from ordinary 



Fig. 30. Bacterium tubei 

 culosis. 



*To accomplish this necessitates a very special and careful proce- 

 dure. Dr. Theobald Smith, of Harvard University (Jour of Exp. Med., 

 Vol. III., 1898, p. 451 ), has the credit of formulating a method by com- 

 bining details in such a manner that the procuring of cultures is, in 

 most cases, possible. Dog serum is used. The method, as he gives it, 

 is as follows : 



" The dog was bled under chloroform and the blood drawn from a 

 femoral artery, under aseptic conditions, through sterile tubes directly 

 into sterile flasks. The serum was drawn from the clots with sterile 

 pipettes and either distributed at once into tubes or else stored with 0.25 



