318 A MANUAL OF BACTERIOLOGY 



hand, expressed the opinion that tuberculous milk fed to 

 children is the main source of infection both of children 

 and of adults ; in the latter case he suggested that bacilli 

 are ingested in childhood and lie dormant for years before 

 becoming active. 



Calmette similarly believes that in the young infection 

 by the digestive tract, especially by tuberculous milk, is 

 the more frequent, and attaches little or no importance to 

 dry dust containing tubercle bacilli as a source of infection. 

 Ravenel considers that the alimentary tract, particularly 

 in children, is a frequent portal of entry for the tubercle 

 bacillus, which he believes is able to pass through an intact 

 mucous membrane. Of sixty cases of human tuberculosis 

 investigated by the Royal Commission on Tuberculosis, 

 twenty- eight possessed clinical histories indicating that 

 in them the bacillus might have been introduced by the 

 alimentary canal. Eraser has also directed attention to 

 the frequency of the bovine type of bacillus in the tuber- 

 culous lesions of bone and joints in children. 



Fliigge, on the other hand, states that his experiments 

 show that tuberculosis can be communicated to animals 

 by inhalation, and that the dose of bacilli required to 

 infect by the respiratory tract is far less than that required 

 to infect by the alimentary canal. The mode of infection 

 in man doubtless varies, and he believes that children 

 may be infected by the digestive tract, by tuberculous food, 

 particularly milk, but the most extensive source of infection 

 is the number of droplets of tuberculous expectoration 

 coughed up by consumptives ; these float in the air and 

 serve as sources of infection to others. Ribbert and 

 Schrotter, also, from the evidence of autopsies, considered 

 inhalation as the chief mode of infection in man. 



Bulloch, 1 from a careful survey of the literature, con- 

 cludes that pulmonary tuberculosis is invariably caused 

 1 " Horace Dobell Lecture," 1910. 



