HOW PARASITIC AND PATHOGENIC BACTERIA REACH MAN 101 
are usually without germicidal properties; at best, their antiseptic 
properties are weak. The removal of bacteria from such surfaces 
is probably for the most part mechanical. The secretion of mucus, 
which has been shown to enclose bacteria, may be an important factor 
in their elimination. 
Movth.— The mouth is a most important portal of entry for the 
great majority of bacteria, both pathogenic and non-pathogenic, 
which are associated with mail. All of the intestinal bacteria, harm- 
ful or benign, many of the bacteria which are associated with morbid 
processes of the respiratory tract, and several which induce specific 
lesions of the brain and spinal cord enter through this atrium. A 
great majority of viruses which infect the respiratory tract and the 
cerebrospinal axis also leave the body through the mouth or nose. 
The normal flora of the mouth is quite varied, ^ including not only 
bacteria which are ordinarily regarded as harmless, but also organisms 
which occasionally or frequently incite disease. Thus, from 20 to 40 
per cent of healthy individuals living in large cities harbor typical 
and apparently virulent pneumococci in their mouths,^ about 2 per 
cent of school children harbor typical diphtheria bacilli in their mouths.^ 
Rarely, tubercle bacilli have been detected in the mouths of apparently 
normal individuals. 
It is worthy of note that an occasional abscess in the cervical region 
may contain spiral organisms; frequently a careful examination will 
reveal a sinus connecting the abscess with the mouth, perhaps origi- 
nating at the base of a carious tooth. Dental caries is usually regarded 
as a bacteriological process. In spite of numerous investigations, 
however, the nature of the process is as 3'et not definitely known. 
It is very probable that lactic acid, formed by the fermentative action 
of bacteria upon residual food particles, plays a not inconspicuous 
part in the solution of the lime salts of the teeth. The etiology of 
pyorrhea alveolaris is also as yet an unsolved, but very important 
infection of the gums. Gilmer and Moody^ have made the important 
observation that streptococci, both of the hemolyticus and viridans 
types, are found in a very large proportion of infected root canals, and 
also in acute and chronic alveolar abscesses. In many instances, par- 
ticularly when communication with the exterior is demonstrable, other 
bacteria are present as well. 
Kordent^ has found hemolytic streptococci in 19.4 per cent of 144 
1 For the older literature and descriptions see Miller: Die Mikroorganismen der Mund- 
hohle, Leipzig, 1892, and Goadby: Mycology of the Mouth, 1903. 
2 Recent observations by Cole and his associates indicate that the ordinary "mouth" 
pneumococci differ in their serological reactions from pneumococci isolated directly 
from pneumonia lesions. 
' Guthrie, Gelien and Moss: Bull. Johns Hopkins Hosp., 1920, 31, 381, have found 
a much larger proportion of diphtheria bacillus carriers during a period when diphtheria 
was epidemic. Many of these were not toxin producers, however. 
* Jour. Am. Med. Assn., 1914, 63, 2023. See also Gilmer: Chronic Oral Infections 
and Their Relation to Diseases in Other Parts, Oral Health, February, 1916. 
s Jour. Dent. Res., March, 1921. 
