PRINCIPLES OF VETERINARY SURGERY 141 



Virulence. — The bacillus tuberculosis has a variable viru- 

 lence dependent largely upon its source. It matters consider- 

 ably whether the source is a particular lesion or a particular 

 species of animals. Those from miliary tuberculosis are 

 very virulent, while those from pulmonary lesions with ul- 

 cerations are generally feeble. The bovine bacillus, gen- 

 erally speaking, is a highly virulent form, and is much more 

 active in the cavy than specimens from human sputum. 



Avenue of Entrance. — The tubercle bacillus enters the 

 body chiefly through the respiratory tract, although its ad- 

 mission via the alimentary canal is now known to be much 

 more common than was once supposed. There is now an 

 overwhelming amount of evidence to prove that ingested 

 milk frequently causes the disease in the human being, as 

 well as in the sucking animal. Wounds on the surface of the 

 body may become the seat of tuberculous processes, al- 

 though this channel cannot be said to be a common one in 

 animals, which fact rather diminishes the importance of 

 tuberculosis in veterinary surgery. The tuberculous, surgi- 

 cal lesion is a rare one in veterinary practice, and is only en- 

 countered, here and there, and under such conditions as pre- 

 clude surgical intervention. 



5. BACILLUS ANTHRACIS.— This bacterium, which 

 was the first specific micro-organism to be recognized as 

 such, causes the disease now universally designated as an- 

 thrax, a fatal infective condition affecting man, oxen, sheep, 

 horses, swine, goats, and the small, laboratory animals. Dogs 

 and cats are generally referred to as immune species, but the 

 observations of several investigators have shown that they 

 may contract the disease by eating rather freely of the car- 

 casses of animals that have died of the disease. The bacillus 

 anthracis was discovered by Davaine in 1850, but it remained 

 for Pasteur and Koch to definitely confirm his discovery by 

 artificial cultivation and inoculation, some years later. 



