In considering the various modes in which infection with the tubercle bacillus can occur, we may, for the purposes of this paper, leave out of discussion all except inhalation and ingestion. There is practically no difference of opinion concerning their relative importance. They play small part in the epidemiology of the disease, and the total number of cases due to them is insignificant compared to those in which infection takes place through the respiratory and the digestive tracts. Both routes of infection are universally recognized, and there remains to be determined now only their relative importance as portals of entry.
Tuberculosis is a disease, the lesions of which are found so preeminently in the lung that it is easy to understand how the older physicians considered the respiratory tract the route of invasion. The classic work of Arnold gave scientific standing to this idea, since it proved that the lung