230 VETERINARY HYGIENE 



slaughtered as diseased, or suspected of being diseased (Diseases 

 Animals Act, 1894, sec. 52). 



TUBERCULOSIS. 



Tuberculosis is a contagious disease of man and animals due 

 to the Bacillus of tuberculosis or Bacillus of Koch. The latter 

 discovered the micro-organism in 1882, but the transmissible nature 

 of the disease had been proved by Villemin in 1865. 



The disease has been known in Great Britain and most parts of 

 the world from a very early date, and at the present time is one of 

 the most wide-spread of animal plagues. M'Fadyean has estimated 

 that in Great Britain between 30 and 40 per cent, of cattle are 

 affected, but its widespread nature was not entirely realised until 

 the discovery of tuberculin. 



Three principle types of tubercle bacilli exist in nature, namely, 

 the so-called bovine, human, and avian types, these differing from 

 one another in pathogenicity and method of growth in artificial 

 culture media. 



From the point of view of the hygienist it is essential to 

 notice : 



(a) That cattle are subject to infection naturally with the bovine 

 type. 



(&) That man may be affected by either human or bovine bacilli. 



(c) That swine are most commonly infected by bovine tubercle 



bacilli. 



(d) Of other animals, the horse as a rule shows infection with 



the bovine type, but commonly also with bacilli which 

 do not strictly belong to either type. 



(e) The dog and cat may show infection with either of the 



mammalian types. 



(/) That farmyard poultry are liable to infection with the avian 

 type. 



No animal is immune to inoculation with one or more of the 

 three principal types of tubercle bacilli. 



The tubercle bacillus is a strictly obligatory parasite. The 

 average temperature in this country is too low to permit of its 

 multiplication outside the body. Even in tropical countries 

 where the temperature is sufficiently high, it certainly does not 

 multiply, since it is difficult to induce it to grow on artificial media, 

 even when these are specially selected. 



The disease is in the majority of cases of a chronic nature and 

 as a rule slowly progressive. Contact between healthy and diseased 



