BACILLUS TUBERCULOSIS. 117 



sputum. It is also found in substances that have been con- 

 taminated with those secretions, and occasionally are wafted 

 in the air in this manner. 



Pathogenesis. The tubercle bacillus is pathogenic for man 

 and for nearly all the lower animals, especially the herbivora, 

 though the carnivora and birds are alike susceptible to it, and 

 traces of the disease have even been found in cold-blooded 

 animals. It may infect the whole animal economy, giving 

 rise to local manifestations in the shape of nodules whicli 

 contain the bacillus. 



The usual mode of infection of animals is through the re- 

 spiratory tract, but sometimes through the gastro-intestinal 

 tract. Infection may occasionally be produced by the intro- 

 duction of the bacilli through abrasions of the skin, as in the 

 case of dissectors or pathologists, when it gives rise to local- 

 ized tuberculous nodules on the hands, which at any time 

 may become the source of infection of the general organism. 



The usual mode of inoculation of animals is either by intra- 

 peritoneal inoculation, when it gives rise to a general tubercu- 

 losis involving especially the glands of the abdomen and the 

 lungs, or by subcutaneous inoculation, when a small quantity 

 of the culture or a small bit of the suspected substance is 

 used. 



The usual contaminating substance for man is the secretion 

 of tuberculous patients, which may be deposited on utensils 

 used by others, or which through carelessness may have dried 

 in the room, thus contaminating the dust of the apartment, 

 which, wafted through the air, is brought into contact with the 

 mucous membrane of the respiratory organs of susceptible 

 individuals. In this way the air of hospital wards of con- 

 sumptives and the various articles of furniture in rooms 

 inhabited by consumptives have been proved to be infec- 

 tious. 



The drinking of contaminated milk and the eating of meat 

 from tuberculous animals are believed in some instances to 

 have spread the disease. This, however, is not thoroughly 

 proved, and recently the eminent Koch has asserted that this 

 mode of contamination is exceedingly rare, and is an equation 



