MICROBIAL DISEASES OF MAN AND DOMESTIC ANIMALS 835 



unity of the tubercle bacterium, and the probability of inter-trans- 

 mission between man and the lower animals. A large number of bac- 

 teriologists now hold that the several types of tubercle bacteria are but 

 environmental variations of the same species. In any case, man clearly 

 appears susceptible to both human and bovine types at least. 



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

 of the digestive tract; it may occur by way of the respiratory organs; 

 it may occur by inoculation; and infection may possibly occur before 

 birth. Some authorities hold that the most common infection is by 

 way of the digestive tract and in early life. Others hold that inhalation 

 tuberculosis is most 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. Toxic substances are 

 produced, as indicated by the fact that killed cultures by subcutaneous 

 injection may destroy local tissues and produce abscess, debility, and 

 emaciation. Production of toxins is indicated by the further fact that 

 certain 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 of this bacterium. One of its constituent products has been re- 

 ported as a fever producer. Another product has been reported which 

 reduces temperature, 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 tuber- 

 cle 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 and which 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 mem- 



