72 IMMUNOLOGY 



by cilia of the epithelium. Undoubtedly the mucous secretions, 

 drainage, rich blood supply, and type of epithelium together with 

 certain phagocytic cells constitute the defensive mechanism of this 

 region. It should be apparent that any interference with the 

 drainage of the sinuses would impair an important defensive 

 mechanism. The paralysis of the cilia by improper treatment or 

 the occlusion of the ducts by swelling of the nasal mucous mem- 

 brane or occlusion by a deviated nasal septum can impair sinus 

 drainage. 



This region of the paranasal sinuses and upper lip is called the 

 "danger area" because the veins draining into the blood sinuses 

 of the head are for the most part without valves and the spread 

 of infection to the blood sinuses would mean the development of 

 meningitis. The proximity of the middle ear to both the mastoid 

 and the lateral sinuses is exceedingly important in the spread of 

 infections. 



Since the roots of the upper teeth (Fig. 1) are in close proximity 

 to the floors of the maxillary sinuses, apical infections may lead to 

 sinus involvement. 



Mechanisms of Infections. — Just how infectious agents are able 

 to penetrate surface barriers is not always clear. Several pos- 

 sibilities are usually suggested as explanations. It is obvious that 

 chemical injury or trauma (mechanical injury) will permit en- 

 trance. Micro-organisms might be taken up by leucocytes present 

 on the surface and these leucocytes might enter the tissues by 

 diapedesis (somewhat as a drop of mercury passes through gela- 

 tin). Yoffey and Sullivan (1939) describe the fixation of vaccine 

 virus by the lymphocytes and the spread of the virus via the 

 cervical lymph ducts to the blood stream. 



If bacteria are able to kill the leucocyte after entering or they 

 escape through disengorgement, it Avould seem logical to assume 

 that the bacteria might be able to grow and develop once they get 

 established. A third possibility is that bacteria may colonize upon 

 the surface and produce substances that kill the epithelial cells 

 adjacent and thus directly find themselves in contact with under- 

 lying structures. Such a condition can be readily visualized as 

 occurring when pathogenic organisms are sealed off within a 

 tonsillar crypt or a hair follicle. Undoubtedly the bacterial protein 

 or the products of bacterial growth frequently affect the perme- 

 ability of the cell membrane. 



