PULMONAEY TUBEKCULOSIS. 17 



this statement is disputed. The unilateral infection is attributed 

 to a weakening of the corresponding half of the larynx due to 

 pressure on the recurrent laryngeal nerve. The nerve is supposed 

 to he involved by the tuberculous process at the lung apex or 

 pressed upon by tuberculous glands in its neighbourhood. The 

 larynx, thus weakened, cannot properly clear itself. The exposed 

 position of the crico-arytenoid joint often leads to its invasion in 

 laryngeal tuberculosis, with consequent fixation of the vocal cord. 



The trachea and main bronchi are protected internally by their 

 smoothness, their ciliated epithelium, and their impermeable 

 basement membranes, but may be invaded from without through 

 the lymphatic glands of the tracheo-bronchial group. 



The lungs are the commonest site of tuberculous infection. 

 The virus is probably air-borne. The terminal air-passages i.e., 

 the terminal bronchioles and the alveoli are forced to rid them- 

 selves of inhaled particles by the slow process of lymphatic 

 drainage, whilst similar particles on the upper parts of the 

 respiratory tract are rapidly removed by the upward current of 

 mucus produced by the ciliated epithelium and fail to pass 

 inwards through the basement membranes. In children the bacilli 

 easily traverse the lung and lodge in the bronchial glands, but 

 in adults, in whom absorption is hindered by the greater firmness 

 of the mucous membrane and possibly also by partial choking of 

 the lymphatics, broncho-pneumonic lesions result, commencing 

 in the terminal bronchioles and extending to the alveoli in 

 connection with them. 



The anatomical causes of the vulnerability of the apices are 

 much disputed. Imperfect blood and lymph circulation, deficient 

 expansion, and deficient expiratory power have all been alleged as 

 causal factors. 



Once established in the lung, the tuberculous focus can spread 

 by various paths. Infection may be carried from the apex of an 

 upper lobe to the apex of a lower or to the opposite lung by 

 aspiration, the infected sputa being inhaled along the short wide 

 bronchus which leads to the apex of the lower lobe, or across the 

 bifurcation of the trachea to the opposite lung. From all 



C.A.A. 2 



