128 TUBERCULOSIS. 



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 which 

 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. 



It has been shown by numerous experimenters that infec- 

 tion by the Bacillus tuberculosis may be induced through the 

 unbroken intestine and no intestinal lesion be manifest. This 

 fact forces the conclusion that infection by way of the ali- 

 mentary tract may be more frequent than heretofore sup- 

 posed. 



Many students of tuberculosis to-day are of the opinion that 

 the greatest proportion of infection is through the alimentary 

 tract. 



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 or swallowed. In this way the air of hospital 

 wards of consumptives and the various articles of furniture 

 in rooms inhabited by consumptives have been proved to be 

 infectious. 



The drinking of contaminated milk and the eating of meat 

 from tuberculous animals are believed in some instances to 



