The mediastinal lymph nodes often become infected in diseases of the respiratory tract, and preeminently so the tracheobronchial groups, which, according to Most,1 receive the lymphatics from the lungs, bronchi, the lower part of the trachea and its bifurcation. In whatever way the micro-organism enters the lung, whether by penetrating the bronchial mucosa near the hilum and spreading in the interstitial tissue and lymphatic system to the lung, as shown in the experiments on monkeys with streptococcus and pneumococcus by Blake and Cecil,2 or hematogenously as demonstrated by Krause3 in experiments with tubercle bacillus in guinea-pigs, the micro-organism ordinarily is carried off from the lungs and bronchi by the lymphatics to the tracheobronchial lymph nodes. The importance of the tracheobronchial nodes as a germharboring depot cannot be overestimated. It has repeatedly been shown that virulent micro-organisms may be present in these lymph nodes without any other demonstrable