Of course artificially-caused ill-health or weakness in parents will
tend in a general way to injure the offspring. But deterioration thus
caused is only a form of quasi-inheritance, as I should prefer to call
it. Semi-starvation in a new-born babe is _not_ truly inherited from its
half-starved mother, but is the direct result of insufficient
nourishment. The general welfare of germs--as of parasites--is
necessarily bound up with that of the organism which feeds and shelters
them, but this is not heredity, and is quite irrelevant to the question
whether particular modifications are transmitted or not.
Another form of quasi-inheritance is seen in the communication of
certain infections to offspring. Not being transmitted by the action of
the organism so much as in defiance of it, such diseases are not truly
hereditary, though for convenience' sake they are usually so described.
A perversion or prevention of true inheritance is also seen in the
action of alcohol, or excessive overwork, or any other cause which by
originating morbid conditions in individuals may also injure the
reproductive elements.
These forms of quasi-inheritance are, of course, highly important so far
as the improvement of the race is concerned. So, too, is the fact that
improved or deteriorated habits and thoughts are transmitted by personal
teaching and influence and are cumulative in their effect. But all this
must not be confounded with the inheritance of acquired characters.
Cases of quasi-inheritance may perhaps be most readily distinguished
from cases of true inheritance by the time test. When a modification
acquired in adult life is promptly communicated to the child in early
life or from birth, it may rightly be suspected that the inheritance,
like that of money or title, is not truly congenital, but is extraneous
or even anti-congenital in its nature. Judged by such a standard, the
inherited injuries in Brown-Sequard's guinea-pigs are only exceptional
cases of quasi-inheritance, and are not necessarily indicative of any
general rule affecting true inheritance.