498 MICROBIOLOGY OF SPECIAL SIGNIFICANCE 



leukocytes. It does not appear to penetrate living tissue. Other 

 mouth amoebae have been described. Whether they really belong to 

 species distinct from Entamcsba buccalis is questionable. Recently it 

 has been claimed that the amoebae of the mouth bear a causal rela- 

 tion to pyorrhea alveolaris, but the claim has not been convincingly 

 proven. 



The various characteristic buccal microorganisms are fotind in 

 particular parts of the mouth and their numbers vary considerably 

 according to the cleanliness of the mouth and teeth, presence or absence 

 of denuded areas, ulcers, sinuses or carious teeth. The iodine^staining 

 varieties are especially abundant between the teeth and upon starchy 

 food residues. The spirochetes, on the other hand, are more abundant 

 in the serum exuding from denuded areas and in pus cavities. B. 

 fusiformis (Vincent) is often found in normal buccal mucus but it is 

 especially abundant in the necrotic ulcers of the tonsil in the disease 

 known as Vincent's angina, in which situation it is always associated 

 with numerous spirochetes. 



Some of the members of the normal mouth flora occasionally play 

 definite pathogenic rdles. There can be little doubt that the starch- 

 fermenting forms produce acid, thus attacking the mineral matter of 

 the teeth and favoring dental caries. The pathogenic r61e of Strept. 

 viridans, when it penetrates into carious teeth, causing root abscess 

 and, probably by metastasis from this focus, giving rise to arthritis and 

 endocarditis, is indicated by a mass of circumstantial and experimental 

 evidence which is well nigh convincing. The frequently serious nature 

 of infections with the hemolytic streptococcus are well known. Doubt- 

 less members of this variety of streptococcus in the mouth are ready 

 to acquire virulence whenever lowered resistance of the host presents 

 a favorable opportunity for them to invade the tonsils, the pharyngeal 

 mucous membrane, the Eustachian tube and middle ear, not to mention 

 more distant parts of the body. 



Certain very specific pathogenic microorganisms are found in the 

 mouth and pharynx from time to time and they sometimes produce 

 lesions there. Spirochceta pallida is especially abundant in the buccal 

 and pharyngeal lesions of secondary syphilis. The tubercle bacillus 

 is expectorated through the mouth in open pulmonary tuberculosis. 

 The pneumococcus is often found in the mouth and pharynx, even in 

 health and is especially numerous and virulent in cases of. lobar pneu- 



