ought and wisdom; but
if we will listen lovingly for her voice, we may be assured that she
will speak to us many a word of cheer and encouragement, of warning
and exhortation. For, to paraphrase the language of the nineteenth
Psalm, "She has no speech nor language, her voice is not heard. But
her rule is gone out throughout all the earth, and her words to the
end of the world."

CHAPTER II

PROTOZOA TO WORMS: CELLS, TISSUES, AND ORGANS

The first and lowest form in our ancestral series is the amoeba, a
little fresh-water animal from 1/500 to 1/1000 of an inch in
diameter. Under the microscope it looks like a little drop of
mucilage. This semifluid, mucilaginous substance is the Protoplasm.
Its outer portion is clear and transparent, its inner more granular.
In the inner portion is a little spheroidal body, the nucleus. This
is certainly of great importance in the life of the animal; but just
what it does, or what is its relation to the surrounding protoplasm
we do not yet know. There is also a little cavity around which the
protoplasm has drawn back, and on which it will soon close in again,
so that it pulsates like a heart. It is continually taking in water
from the body, or the outside, and driving it out again, and thus
aids in respiration and excretion. The animal has no organs in the
proper sense of the word, and yet it has the rudiments of all the
functions which we possess.

A little projection of the outer, clearer layer of protoplasm, a
pseudopodium, appears; into this the whole animal may flow and thus
advance a step, or the projection may be withdrawn. And this power
of change of form is a lower grade of the contractility of our
muscular cells. Prick it with a needle and it contracts. It
recognizes its food even at a microscopic distance; it appears
therefore to feel and perceive. Perhaps we might say that it has a
mind and will of its own. It is safer to say that it is irritable,
that is, it reacts to stimuli too feeble to be regarded as the cause
of its reaction. It engulfs microscopic plants, and digests them in
the internal protoplasm by the aid of an acid secretion. It breathes
oxygen, and excretes carbonic acid and urea, through its whole body
surface. Its mode of gaining the energy which it manifests is
therefore apparently like our own, by combustion of food material.

[Illustration: 1. AMOEBA PROTEUS. HERTWIG, FROM LEIDY.
_ek_, ectosarc; _en_, endosarc; _N_, food particles;
_n_,