A ship arriving from an infected port, plague-infected rats found in a previously healthy
locality, a traveller arriving by land or sea from a district or town in which plague is raging, may
each and all prove to be the cause of an outbreak of the disease. The spread of the disease
in a healthy town may be distinctly traced to its origin and focussed upon a particular house, as has
been the case in Glasgow. How the disease reached the abode in question in Glasgow has not yet been
ascertained, but that in one particular household the disease primarily developed and infected others
is an undoubted fact. The importance of tracing the infection to a focus will be understood by a
study of the means by which plague is spread. So far as is known it is largely by human intercourse
that the plague is spread, and with this fact in view the question of dealing with all persons who have
been in contact with plague-infected persons is simplified. All " contacts ' must be isolated until the
period of incubation is over. This is perhaps the most important point to be remembered by medical
men and public authorities in their attempt to limit or to stamp out the disease.
The means by which plague is spread—Plague is spread chiefly by human agency; but rats,
body and household parasites, wounds, food and drink, and infection by the air are all possible
agents in the spread of the disease.
Contact with plague-infected persons may or may not directly influence infection by plague; all
depends on the circumstances and environment. Doctors, nurses, and attendants in hospitals are not
markedly subject to attack, in fact the plague hospital seems to be the one place in a plague-stricken city
where contagion is least potent. This is to be accounted for by the cleanliness of hospitals and by the care
taken to disinfect clothing, bedding, utensils and excreta. In uncleanly abodes where disinfection,
&c., is not practised, contact with persons sick of plague is dangerous in the extreme. Plague germs
leave the body by way of the respiratory tract, by the fasces and by the urine. The sputum is the
most directly infectious of all these, but the excreta are more likely to convey the bacillus either by
soiling the clothing, the bed-room furniture, or by inoculating rats and other vermin.
Faeces are found to contain plague bacilli for four weeks after the crisis of the illness has passed,
and the danger of convalescent patients mixing with the community is thus readily understood.
Clothing soiled by vomited or expectorated matters, by faeces or urine, retains infective powers
for some time (months) if packed away whilst yet moist.
Food, such as grain, fruit, &c., has been found impregnated with plague bacilli, but proof that
food or water has directly conveyed infection is wanting.
Rats are very prone to plague. The first warning that plague is incident may be deaths
amongst rats. Plague-infected rats leave their runs, they appear dazed, become seized with convulsions
and speedily die. Whether the rat is seized with plague before man and thus infects him,
or whether man infects the rat, is a question as yet undecided. Many epidemics are believed to
have been traced to rats, yet in other localities, and markedly so in Glasgow, the rats have not been
found infected by plague, either before or after the outbreak. It is by the vermin in the rat's coat that
infection is probably conveyed to man. The vermin leave the rat soon after the animal dies, and as it
is found that the vermin contain the bacilli, the poison may gain entrance to the human body by
vermin bites or by the abrasion of skin consequent on the scratching they induce.
Parasites, such as fleas, bugs, and lice, acquire the bacillus from feeding on plague-sick persons,
or they may gather it from clothing, bedding, &c., soiled by excretions.
Infection by the air is open to question, as although the bacillus has occasionally been found
in the dust of rooms, on earthen floors, and even on the walls, it has never been isolated from the air.
It is conceivable, however, that in an ill-ventilated room the atmosphere may become so impregnated
with the emanations from the sick as to become infectious of itself.
Entrance to the body—The plague bacillus may gain entrance by the skin, and possibly by
the breath and the mouth. Entrance by the skin is considered probable for several reasons. In
the first place it is the groin (femoral) glands that are most usually the seat of buboes. The
selection of this group is frequently attributed to the fact that the majority of persons affected by
plague in warm countries go bare-footed. Against this conclusion are the facts that skin abrasions
are but seldom found, and that persons not going bare-foot have their groin glands most
frequently attacked. The axillary glands, affected by way of the hands, would a priori seem to be
more liable to such a method of inoculation seeing the hands are exposed and that soiled articles,
dead bodies, rats, &c., are touched by them. Such, however, is not the case. It is possible, however,
that if vermin are the intermediaries of contagion that they could settle more quietly and undisturbedly
on the lower extremities, even beneath the garments, than on the more exposed parts such as the
hands or face, where they are liable to be disturbed or brushed off.
Plague has been acquired by post-mortem wounds, by the sputum alighting on the conjunctiva,
and in many instances the marks of insect bites and scratchings on the lower limbs would point to the
skin as being the medium of entrance to the body.
Cracks in the lips and inflamed tonsils are assumed to be the mode of entrance of plague
poison when the cervical glands are primarily enlarged. Proof that the bacillus can be inhaled, or
that the body may be contaminated by the alimentary canal, is wanting, and however much these
channels may swarm in bacilli, the mere fact does not prove that they were infected directly from