on of an animal or plant when
taken into a new environment, removed from conditions which held it in
check, as the introduction of the mongoose into Jamaica, the rabbit
into Australia, the thistle into New South Wales and the water-plant
chara into England.

It is very difficult to say, but it seems as though there is an
increasing unevenness in the distribution of wealth, an increase in
the number of persons who live at the expense of the laboring class.
Mass labor, effective though it be, makes it easier to divert the
proceeds of labor from the laborers. The evidence of this is seen in
the increase in number and the prosperity of those pursuits which
purvey to luxury, as the automobile industry and the florists' trade
and the greatly increased scope and activity of the social game. On
the other hand, there is an increase in the number of people who are
to a greater or less extent dependent upon extraneous aid, evinced
among other ways by the increase in the asylum populations. Both these
conditions, wealth and poverty, are important disease factors.
Tuberculosis is now a disease of the proletariat chiefly. The measures
both of prevention and cure can be and are carried out by the
well-to-do, but the disease must remain where there are the conditions
of the slums. Of all the conditions favoring infant mortality poverty
comes first. In Erfurt, a small city of Germany, of one thousand
infants born in each of the different classes, there died of the
illegitimate children three hundren and fifty-two; of those of the
laboring class, three hundred and five; of those in the medium station
(official class largely), one hundred and seventy-three; of those in
higher station, eighty-nine. The same relation of infant mortality to
poverty becomes apparent when estimated in other ways. In Berlin, with
an average infant mortality of one hundred and ninety-six per
thousand, the deaths in the best districts of the city were fifty-two
and in the poorer quarters four hundred and twenty. The effect of
poverty is seen particularly in the bottle-fed infants; with natural
nursing the child of poverty has almost as good a chance as the child
of wealth. From reasons which are almost self-evident, the mortality
in illegitimate infants is almost double that of the legitimate. The
greater infant mortality in poverty is due to the more numerous
children preventing individual care, the separation of the mother from
the nursing child in consequence