addition to qualities which come from each
ancestor, and from remote ancestors through these. The qualities with
which the new organism starts are those which it has received from its
ancestors plus its individuality. The fact that the sexual cells are
formed from the early formed cells of the new organism which represent
all of the qualities of the fertilized ovum or primordial cell,
renders it unlikely that the new offspring will contain qualities
which the parents have acquired. The question of the inheritance of
characteristics which the parents have acquired as the result of the
action of environment upon them is one which is still actively
investigated by the students of heredity, but the weight of evidence
is opposed to this belief.

In the new organism the type of the species is preserved and the
variations from the mean to which individuality is due are slight. We
are accustomed to regard as variations somewhat greater departures
from the species type than is represented in individuality, but there
is no sharp dividing line between them.

Very much wider departures from the species type are known as
mutations. Such variations and mutations, like individuality, may be
expressed in qualities which can be weighed and measured, or in
function, and all these can be inherited; certain of them known as
dominant characteristics more readily than others, which are known as
recessive. If these variations from the type are advantageous, they
may be preserved and become the property of the species, and it is in
this way that the characteristics of the different races have arisen.
Certain of the variations are unfavorable to the race. The varying
predisposition to infection which undoubtedly exists and may be
inherited represents such a variation. Tuberculosis is an instance of
this; for, while the cause of the disease is the tubercle bacillus,
there is enormous difference in the resistance of the body to its
action in different individuals. The disease is to a considerable
extent one of families, but while this is true the degree of the
influence exerted by heredity can be greatly overestimated. The
disease is so common that in tracing the ancestry of tuberculous
patients it is rare to find the disease not represented in the
ancestors. A further difficulty is that the environment is also
inherited. The child of a tuberculous parent has much better
opportunity to acquire the infection than a child without such an
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