98 SAPROPHYTISM, PARASITISM AND PATHOGEN ISM 
genitalia, are good culture media for certain acid-fast bacteria, par- 
ticularly B. smegmatis. The cerumen of the external ear is frequently 
infected with Micrococcus cereus flavus, and the puncture of the tym- 
panic membrane may lead to direct infection of the middle ear from 
the outside, with this or other organisms. Infection of the middle ear 
may also take place directly through the Eustachian tube. The blood 
and lymph may also deposit bacteria in the middle ear. 
The conjunctiva, by virtue of its very exposed position, must 
receive bacteria upon it very frequently. Its polished surface and 
the mechanical cleansing by the flow of tears (which do not possess 
germicidal properties) usually suffice to remove adventitious bac- 
teria and to prevent bacterial development under ordinary conditions. 
Maxcy^ and Corper and Enright- have studied experimentally the 
elimination of certain non-pathogenic bacteria from the conjunctival 
sac. It was found that some of the organisms could be found in the nose 
within fi\'e minutes, the throat within fifteen minutes, and the feces 
in twenty-four hours. Most of the bacteria leave the body with the 
feces, but they may persist in the larynx and trachea for several days. 
The conjunctival sac, which receives the washings from the con- 
junctiva, is probably the recipient of many bacteria; of these B. 
xerosis occurs with sufficient regularity in the conjunctival sac to be 
regarded as a normal inhabitant. The pneumococcus is also found 
there. These organisms are "opportunists," occasionally causing 
severe acute conjunctivitis, although usually they are benign. Certain 
bacteria aft'ect the conjunctiva fairly readily. Among these organisms, 
the gonococcus is particularly troublesome, causing a most severe 
inflammation. Ophthalmia neonatorum, a gonorrheal infection of 
the conjunctivae of the new-born of infected mothers, has been in the 
past a very common cause of blindness. It has been claimed that 
the meningococcus may occasionally pass from the eye through the 
tear duct to the nasal cavity, and from there to the meninges. 
Snhcntaneous Tissue.— Wa\\\ bacteria, particularly exogenous path- 
ogenic bacteria, do not develop in the subcutaneous tissues. This 
is true for a majority of those organisms which induce specific pro- 
gressive disease from man to man, such as typhoid and cholera bacilli. 
On the other hand, many of those bacteria which are habitually para- 
sitic on the skin may produce infections of the subcutaneous tissues 
which vary in severity from mild inflammations to severe cellulitis. 
The staphylococci and streptococci are among the more important of 
this type. 
Tonsils.^— ^he crypts of the tonsils afford mechanical protection 
to bacteria which gain access to them, and the secretions and tissue 
undoubtedly provide the necessary nutritive elements, consequently 
it is not sm-prising to finfl many types of bacteria there. Staphylo- 
' Jour. Am. Med. Assn., 1919, 72, 636. ^ ibid., 1920, 74, 521. 
3 Davis: The Tonsil in Relation to Infectious Processes, Jour. Am. Med. Assn., 1920, 
70, :u7. 
