HOW PARASITIC AND PATHOGENIC BACTERIA REACH MAN 95 
intestinal tract, the nrinary tract or the skin) bacteria which are 
capable of inciting disease in others. Such individuals are known 
as bacillus carriers; frequently they eliminate these pathogenic bacteria 
in large numbers. 
The bacillus carrier may or may not give a history indicating 
recovery from an infection of the specific organism which he "carries." 
Bacillus carriers may be temporary carriers, in which event they harbor 
the pathogenic bacteria for but a few weeks, or they may become 
habitual carriers, in which case the organism may be excreted for con- 
siderable periods of time, even years. The excretion may be constant 
or intermittent. 
The typhoid bacillus is a common organism to be thus carried. It 
appears to localize eventually in the gall-bladder or the bile ducts, 
less commonly in the urinary bladder, and it may appear occasionally 
in large numbers in the feces or urine of the carrier. Women are 
more commonly found to be typhoid carriers than men. Similarly, 
paratyphoid, dysentery and cholera organisms may be excreted in 
the feces through long periods of time, rarely or never, however, in 
the urine. 
Slowly progressing focal diseases, as pulmonary tuberculosis are, 
in a sense, spread by carriers, for the patient may survive for years, 
excreting daily large numbers of tubercle bacilli. The line of demar- 
cation, in other words, between the human bacillus carrier and the 
patient in whom a focal disease is chronic for long periods of time is 
not sharply circumscribed. 
7. Contact Infection.— The direct transmission of bacteria from man 
to man is well exemplified in the venereal diseases, gonorrhea and 
syphilis, which are usually transmitted by direct contact. Diseases 
of the respiratory tract, as tuberculosis, diphtheria and whooping 
cough, may be transmitted directly from patient to patient by kiss- 
ing, swapping chewing gum, by eating utensils, etc. Soiled fingers 
may transmit the typhoid bacillus from a typhoid patient to other 
individuals. All of the excrementitious diseases may be spread in a 
similar manner, under certain conditions. 
The transmissions of respiratory diseases by hand-to-mouth through 
the agency of improperly cleansed mess-kits^ and spoons, knives and 
forks,- has received considerable attention since the studies upon 
modes of infection in army camps have been published. It appears 
that hand-to-mouth infection may be a material factor in the spread 
of respiratory infections. 
8. Germinal and Prenatal Infection.— True germinal infection implies 
that a disease-producing microorganism is carried l)y the ovum or 
spermatozoa and incorporated in the embryo prior to its development. 
This method of transmission is not definitely worked out, although it 
Lynch and Cumming: Am. Jour. Pub. Health. 1919, 9, 25. 
Gumming: Jour. Am. Med. Assn., 1920, 74, 1072. 
