PARASITES AND DISEASE (VEGETABLE PARASITES) 167 

 TUBERCULOSIS 



Definition. An infective disease caused by the Bacil- 

 lus tuberculosis. So termed because of the formation in 

 its lesions of small nodular bodies called tubercles. 



Etiology. There is perhaps no disease to which the 

 animal kingdom is more universally susceptible. It is 

 transmitted by means of the secretions of susceptible 

 animals. Cattle, hogs, and man are the most suscep- 

 tible; rabbits and guinea-pigs less so; as are also cats 

 and dogs, which are, however, sometimes infected by 

 tuberculous masters. Monkeys appear to be immune 

 in the wild state, but exceedingly susceptible in captiv- 

 ity, bearing out the fact that tuberculosis is a house- 

 bred disease. 



Heredity was formerly considered an important pre- 

 disposing cause, it being thought than an increased sus- 

 ceptibility was transmitted from parent to offspring. 

 It is probable that this is greatly overestimated, and 

 that, indeed, in case of parents who have recovered from 

 tuberculous infection a certain degree of immunity or 

 increased resistance to infection is transmitted to the 

 offspring. The most important predisposing causes 

 are overwork, underfeeding, and poorly ventilated liv- 

 ing quarters. There is perhaps no disease in which the 

 susceptibility is so increased by bad living, debilitating 

 diseases, as measles, whooping-cough, pneumonia, grip, 

 etc. 



The modes of infection are inhalation, ingestion (in 



