MICROBIAL DISEASES OF MAN AND ANIMALS. 629 



There has been great difference of opinion concerning the unity of the 

 tubercle bacterium, and the probability of inter-transmission between 

 man and the lower animals. A large number of bacteriologists now 

 hold that the several types of tubercle bacteria are but environmental 

 variations of the same species. 



The entrance of the germ may occur in four ways, namely, by way of 

 the digestive tract with food or drink; it may occur by way of the respi- 

 ratory organs with inspired air; it may occur by inoculation; and in- 

 fection may possibly occur before birth. Good authorities hold that 

 the most common infection is by way of the digestive tract and in early 

 life. Inhalation tuberculosis is also regarded as very common. 



This bacterium produces a slow toxaemia, and it is this toxaemia to- 

 gether with physical embarrassment of the vital organs by extensive lesions 

 which together harm the affected body. Various toxins are produced, as 

 indicated by the fact that killed cultures by subcutaneous injection 

 destroy local tissues and produce abscess, debility, and emaciation. 

 Production of toxins is indicated by the further fact that an antitoxic 

 immunity may be produced by minute doses of killed culture gradually 

 increased. 



Tuberculin is a common and well known product or mixture of pro- 

 ducts produced by this bacterium. One of its constituent products is a 

 fever producer. Another product has been recognized which reduces tem- 

 perature, and still another which produces convulsions, in sufficient dose. 



Tuberculosis may be very general. Almost any tissue or organ in the 

 body may be invaded; but, as a rule, not many organs are badly affected 

 in the same case. Distribution occurs by way of both the blood and 

 lymph streams, especially the latter. It seems probable that tubercle 

 bacteria may be distributed in the body by wandering phagocytes. 



The Bad. tuberculosis has a characteristic tendency to produce tuber- 

 cles or nodules which may be large or small ; they have a tendency to 

 central necrosis and degeneration. Mucous membranes, under this 

 infection, tend to develop superficial ulcers. 



The lesions produced by this microorganism may vary from the 

 tiniest tubercles to extensive areas of large organs. Lymph glands 

 frequently enlarge and undergo cheesy or calcareous degeneration. 

 Tubercular masses of various sizes may appear upon the lining 

 membranes of the chest and abdominal cavities and upon various inter- 

 nal organs. Cheesy abscesses may appear in the depths of soft organs. 



