CHANNELS OF INFECTION 387 



Numerous researches indicate that primary pulmonary 

 tuberculosis is not only possible by the lymphatic and 

 vascular channels, but that infection is generally communi- 

 cated by these routes. This is the view of Behring, 

 Ravenel, Calmette x and many others. The bacilli are 

 absorbed by the lymphatic or blood vessels of the buccal, 

 pharyngeal or intestinal mucous membrane and are 

 carried to the alveoli or to the peri -bronchial lymphatics. 

 The circum-pharyngeal ring of lymphatic tissue may be 

 regarded as a protective barrier, to a considerable extent 

 limiting infection by air-borne pathogenic organisms. 

 As regards infection of the lungs by the vascular route, 

 this is brought about by the arrest in the alveolar or 

 peri-bronchial blood capillaries of leucocytes which have 

 ingested tubercle bacilli recently introduced into the body 

 by the alimentary tract, or derived from a latent focus of 

 infection, more or less old, and becoming the site of giant- 

 cell formation. As Calmette says : "In all animals, 

 including man, which are susceptible, tuberculosis in all 

 regions, lymphatic glands, lungs, etc., especially in those 

 forms which develop slowly, results in the vast majority 

 of cases from a primary lymphatic, or less frequently 

 blood, infection, having as its origin the absorption of 

 tubercle bacilli by the alimentary tract, principally by 

 the buccal, pharyngeal and intestinal mucous membranes." 



In 1919 the deaths from pulmonary tuberculosis in 

 England and Wales numbered 36,662, while those from 

 other forms of tuberculosis were only 9,650, so that the 

 greater part of the mortality from tuberculosis must be 

 ascribed to infection with the human bacillus derived 

 from human sources. Of the non-pulmonary tuberculosis 

 deaths, a portion is caused by the bovine bacillus, which 

 may probably be principally ascribed to infection by 



1 L'Infection Bacillaire et la Tuberculose, 1920. An excellent summary 

 of the subject is given in this work. 



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