tUfiERCULOSTS. 68J5 



of the identity of tuberculosis in mammals still appears probable, in 

 spite of the recent declarations of Koch (1901). 



Causation. Tuberculosis is due solely to the activity of the 

 tubercle bacillus. In 1884 Koch isolated and cultivated this bacillus 

 in living animals, and always reproduced typical tuberculous lesions 

 by injecting cultures. In 1887 Nocard and Koux described a rapid 

 method of cultivating the bacillus, and in 1890 Koch announced the 

 discovery of tuberculin. 



The tubercle bacillus assumes the form of a little rod, five or six 

 micro-millimetres in length, and '03 to '05 /x in thickness. It has a 

 special staining reaction when treated with Ehrlich's or Ziehl's 

 solution. It grows between 98° and 104° Fahr. (37° and 40° C.) in 

 various artificial media containing glycerine. 



Healthy subjects become infected by the accidental entrance of 

 germs into their bodies, either by the respiratory and digestive tracts, 

 or through- solutions of continuity in the skin. 



The material from tuberculous centres is virulent, whether con- 

 sisting of sputum or discharge, saliva, faeces, urine, milk, etc., or 

 tuberculous tissues derived from the different viscera. 



The blood and muscular tissues are not always virulent, even in 

 cases of generalised tuberculosis. 



The virulent organisms usually enter the body through the lym- 

 phatic system; invasion proceeds from the point inoculated towards the 

 nearest lymphatic glands and thence along the chain of lymphatic 

 vessels, and the lesions extend, attacking the internal organs more 

 or less rapidly. The body does not necessarily become fatally in- 

 fected as a consequence of accidental or even experimental infection, 

 for the bacillus may itself be destroyed by the phagocytes, or the 

 lesion may remain purely local. 



Although tuberculosis is the gravest and most widespread disease 

 on the surface of the globe, its contagious character is relatively little 

 marked, a fact which has unfortunately led to its receiving little 

 attention in ordinary life. 



Contagion is usually the result of cohabitation, although contact 

 between diseased and healthy subjects for a period of some days or 

 even weeks does not seem sufficient to produce the disease. Nocard 

 has fixed a mean period of five to six months as necessary for the 

 contraction of the disease by bovine animals, and Moussu has arrived 

 at almost identical results by placing tuberculous and healthy cows 

 together in a byre reserved for such researches. In this connection, 

 however, very great differences of individual susceptibility exist, and 

 these are difficult to appreciate in the present state of our knowledge. 

 It thus happens that an animal of vigorous appearance and in good 



