CHAPTER XLVII 

 BACTERIA OF THE RESPIRATORY TRACT 



D. J. DAVIS 



University of Illinois College of Medicine, Chicago 



ECOLOGICAL RELATIONS 



In the respiratory passages of the normal newborn, no bacteria are found. Within 

 a few hours organisms of various kinds enter and continue to inhabit these regions in 

 relatively large numbers throughout life. Neither in numbers nor in variety are they 

 uniformly distributed. Certain bacteria tend to localize in certain regions. Anatomi- 

 cal and physiological conditions are no doubt the important ecological factors in this 

 normal distribution. Among such factors we may mention moisture; temperature; 

 the existence of deep pockets or crypts in the mucosa; smooth or rough surfaces with 

 pits, furrows, or grooves; the oxygen supply as determined by anatomic peculiarities 

 in the respiratory passages; acid, neutral, or alkaline reaction of the tissue and secre- 

 tions; narrow or wide channels; ciliary action; the deposition of food and foreign par- 

 ticles in certain localities; artefacts and alterations resulting from injuries, operations, 

 pathological states, etc. 



As a consequence, there have appeared in various regions of the respiratory tract 

 more or less characteristic floras which have adapted themselves to the conditions pre- 

 vailing there; for example, a nasal flora, buccal flora, tonsil flora, teeth flora, pharyn- 

 geal flora, etc. The nasal passages become inhabited chiefly by a moderate number 

 of coccal organisms, both gram positive and gram negative; the buccal mucosa largely 

 by gram positive diplococci; the surface of the tonsil by gram positive diplococci; and 

 the crypts of the tonsils by a variety of organisms both aerobic and anaerobic, quite 

 unlike those of the surface. The pharynx harbors chiefly large numbers of gram 

 positive and gram negative organisms, diphtheroids, cocci, and bacilli. Below the 

 larynx the numbers of organisms rapidly decrease, and in the deeper channels leading 

 to the lungs proper only transients are found normally. After the teeth erupt, the 

 mouth becomes more heavily infected with certain bacteria, especially fusiform ba- 

 cilli and spirochetes of several kinds. These organs have much to do in maintaining 

 a high bacterial content in the mouth throughout life. Especially is this true in in- 

 dividuals with teeth and gums in that pathological state which in most civilized peo- 

 ple is the rule rather than the exception. As the teeth disappear in old age, the mouth 

 becomes less heavily contaminated. 



LYMPHOID TISSUE AND BACTERIA 



There appears to be an interesting relation between the distribution of bacteria 

 and the distribution of lymphoid tissue in certain channels of the body, especially 

 the respiratory tract. Lymphoid tissue occurs, generally speaking, only in localities 

 where absorption is taking place; for example, the clusters of lymphatic glands at the 



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