CONSUMPTION OF THE LUNGS. 221 



\re are not warranted in denying the possibility of a chilling of the 

 Btomach having the same effect. 



Numerous examples exist in the practice of every experienced 

 physician, in which the cough has commenced on some particular day 

 following a severe cold, soon after which the other symptoms of con- 

 sumption have made their appearance. 



A proof of the extremely important role played by the presence 

 of foreign substances in the air-passages, as an exciting cause of con- 

 sumption, is found in the great prevalence of the malady among opera- 

 tives and other persons who constantly live in a dusty atmosphere, 

 such as stone-cutters, file-grinders, hatters, wool-carders, cigar-makers, 

 etc. Of all foreign bodies which, by irritation of the bronchial walls, 

 and of the pulmonary substance itself, give rise to consumption, the 

 blood which is retained in the air-vesicles and bronchi after a haemop- 

 tysis or pneumorrhagia most frequently has that effect, as we have 

 already explained while treating of bleeding from the bronchi and lungs. 



Having discussed the etiology of the pneumonic process which 

 plays the most important role in the production of pulmonary phthisis, 

 we must now add a few words regarding the etiology of pulmonary 

 tuberculosis. 



The development of tubercles in the lung, without the preexistence 

 of caseous degeneration of the inflammatory products, is less common 

 in chronic pulmonary tuberculosis, which is complicated with chronic 

 pneumonia, and terminates in consumption, than in acute miliary tuber- 

 culosis (see Chapter XIV.). The etiology of these exceptional cases 

 is utterly obscure, although it would seem that persons predisposed to 

 inflammation, ending in caseous degeneration, suffer from prit.iary 

 tuberculosis of the lung, in the stricter sense of the word, with greater 

 relative frequence. 



The caseous masses, upon which the consecutive (secondary) devel- 

 opment of tubercles in the lungs depends, are situated, in the great ma- 

 jority of cases, in the lungs themselves, and consist of the products of 

 chronic pneumonia, in a state of caseous degeneration. We have no 

 hesitation in stating that the greatest danger, for the majority of con- 

 sumptives, is, that they are apt to become tuberculous. The conditions 

 which cause tuberculosis to accompany many cases of caseous infiltration 

 with formation of cavities, but not all such cases, and the reason why 

 the complication is sometimes early and sometimes late in its appear- 

 ance, are at present unknown to us, but it seems that incapsulation of the 

 caseous mass affords a certain degree of protection against tuberculosis. 



Next to the caseous products of pneumonia, the exudation of pleu- 

 risy and pericarditis in a state of caseous degeneration, and bronchial 

 glands in similar condition, most frequently give rise to tuberculosis. 



