206 STUDIES IN ADVANCED PHYSIOLOGY. 



PATHOLOGICAL CONDITIONS OF THE RESPIRATORY SYSTEM. 



While there is not a single system in the body which is 

 immune from the attacks of disease, and though in many 

 individuals the respiratory system is among the most invul- 

 nerable, yet the general fact remains that this system more 

 than any other becomes the seat of pathological conditions. 

 This system is especially apt to become congested and in- 

 flamed as a consequence of exposure to cold. When this 

 inflammation is limited to the trachea, the bronchial tubes 

 and its larger divisions, we speak of it as a mere cold on 

 the chest, or bronchitis. As a consequence of a congested 

 condition of the respiratory mucous membrane it frequently 

 becomes sore, and is marked by an excessive secretion of 

 mucus, often to such an extent as to more or less clog 

 the passages. This excessive mucus is, of course, the 

 familiar phlegm, which forms such an annoyance of an 

 ordinary cold. Possibly the meaning of this extra mucous 

 secretion may be found in the fact that it acts as a kind of 

 protection to the inflamed membrane beneath, and serves 

 to prevent the introduction into that membrane of foreign 

 particles, be they ordinary grains of dust or more injurious 

 germs. This phlegm is, therefore, figuratively speaking, 

 a kind of natural salve which nature puts over these con- 

 gested portions to prevent the danger of exposure to foreign 

 elements. 



This congestion may also extend into the air passages of 

 the nose and so produce the familiar " cold in the head," 

 and as the mucous membrane of the pharynx is continued 

 into the middle ear through the Eustachian tube, that organ 

 is frequently drawn into the inflammation. When such a 

 congestion of the nasal passages continues and becomes the 

 seat of ulcerations, it leads to the too-common catarrh. 

 But the term " catarrh " is not, strictly speaking, confined 

 in its application to a chronic inflammation of the nasal pas- 

 sages. The term "catarrh" means inflammation, and in 

 such a sense is applied to an inflammation wherever it may 

 occur. Thus, bronchitis is but a catarrh of the bronchial 



