Page 87 - My FlipBook
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of the forms of plants during the winter season, life seems
dormant ; but when the spring comes, and the conditions
of growth return, these chemical changes must begin or else
life becomes extinct. When the seed is placed in the condi-
tions for growth these chemical changes must begin or else
the seed dies. So with the egg; when it is placed under con-
ditions for incubation, the chemical changes necessary to the
life of the chick or of the animal, whatever it may be, must
proceed or the egg dies. So with the spore, and so on.
These chemical changes are absolutely necessary to the con-
tinuance of life.
For our purpose a very simple examination of these will
be sufficient. The essential features of the physiology of ani-
mals, plants and microbes are practically the same, and as
you have been over the physiology of man it will be easy,
I hope, for you to follow me.
We may reduce the number of functions to be examined
to four, and these are often spoken of as the vegetative func-
tions. They are
—
First *'The power of digestion," or preparation of food
for absorption.
Second—The power of assimilation, or the power of the
appropriation of food material to tissue building.
Third—The power of the formation of waste products,
or the shedding out of material once used.
Fourth—The power of reproduction in a definite line of
forms.
Every form of life must be capable of performing these
four functions ; life cannot continue to exist without them in
any form whatever. It is true some of the parasites may
appropriate food that has been prepared by the plant or the
animal upon which, or in which, they grow, but sometime
during the life of that parasitic plant it must digest its own
food, and generally it does digest its own food before it is
appropriated to its use, not taking it in the form in which
it is furnished by the plant on which, or the animal in which,
it is parasitic.
The power of reproduction in a definite line of forms is
generally taken by naturalists as the test of life. If there is
a substance of which there is a question as to whether it is
living matter or not, the test is : Will it reproduce itself in
75
of the forms of plants during the winter season, life seems
dormant ; but when the spring comes, and the conditions
of growth return, these chemical changes must begin or else
life becomes extinct. When the seed is placed in the condi-
tions for growth these chemical changes must begin or else
the seed dies. So with the egg; when it is placed under con-
ditions for incubation, the chemical changes necessary to the
life of the chick or of the animal, whatever it may be, must
proceed or the egg dies. So with the spore, and so on.
These chemical changes are absolutely necessary to the con-
tinuance of life.
For our purpose a very simple examination of these will
be sufficient. The essential features of the physiology of ani-
mals, plants and microbes are practically the same, and as
you have been over the physiology of man it will be easy,
I hope, for you to follow me.
We may reduce the number of functions to be examined
to four, and these are often spoken of as the vegetative func-
tions. They are
—
First *'The power of digestion," or preparation of food
for absorption.
Second—The power of assimilation, or the power of the
appropriation of food material to tissue building.
Third—The power of the formation of waste products,
or the shedding out of material once used.
Fourth—The power of reproduction in a definite line of
forms.
Every form of life must be capable of performing these
four functions ; life cannot continue to exist without them in
any form whatever. It is true some of the parasites may
appropriate food that has been prepared by the plant or the
animal upon which, or in which, they grow, but sometime
during the life of that parasitic plant it must digest its own
food, and generally it does digest its own food before it is
appropriated to its use, not taking it in the form in which
it is furnished by the plant on which, or the animal in which,
it is parasitic.
The power of reproduction in a definite line of forms is
generally taken by naturalists as the test of life. If there is
a substance of which there is a question as to whether it is
living matter or not, the test is : Will it reproduce itself in
75
