rary, many infections run a particularly severe course
in strong and healthy subjects, and, contrariwise, may be
mild and benign in the feeble. Physical weakness,
therefore, is not necessarily synonymous with increased
susceptibility to all infections, although true for some of
them. In other words, 'general debility' lowers resistance
in a specific, rather than in a general, sense."--(Rosenau:
Preventive Medicine and Hygiene, pp. 403 and 404.)

CARRIERS

Well persons who carry in their bodies pathogenic germs but who
themselves have no symptoms of disease are called carriers. Thus typhoid
carriers have typhoid bacilli in the intestinal tract, while they
themselves show no symptoms of typhoid fever; diphtheria carriers have
bacilli of diphtheria in the throat or nose, but have themselves no
symptoms of diphtheria, and so on. It has now been proved that many
patients harbor bacteria for weeks, months, or even years following an
infection, and are dangerous distributors of disease; also, some
healthy individuals without a history of illness harbor living bacteria
which may infect susceptible persons in the usual ways. Transmission by
healthy carriers goes far to explain the occurrence of diseases among
persons who have apparently not been exposed. This explanation has
greatly clarified the whole problem of the spread of communicable
diseases. Carriers, unfortunately, exist in large numbers, and render
the ultimate control of disease exceedingly difficult. They can usually
be identified by bacteriological tests. To some extent they can be
supervised; food handlers at least should be legally obliged to submit
to physical examinations, and should be licensed only when proved free
from communicable disease.

Diseases are also spread by persons suffering from them in a form so
mild or so unusual that they pass unrecognized. These persons are known
as "missed" cases. Carriers of disease and "missed" cases go freely
about the community, handling food, using common drinking cups,
travelling in crowded street cars, standing in crowded shops; in various
ways coming into close contact with other people, coughing and sneezing
and kissing their friends no less often than normal individuals. It is
consequently clear that the bodily discharges of supposedly normal
persons may be hardly less a menace than those of persons known to be
infected.

Diseases that depend for transmission upon mi