Page 89 - My FlipBook

the active secretions. In this the chemical forms are
changed. Take the chemical forms of starch or sugar or
various other of the foods which we eat, and we find they
are very simple, composed of a few combining equivalents,
but when we come to examine the combining equivalents
in the formation protoplasm we find it is composed of a large
number of each of the elements entering into the formation
of a single molecule, and this is characteristic of the com-
pounds formed by the life force, the molecules being com-
posed of large numbers of equivalents of the elements. Then
this is nutrition—the process of digestion and nutrition as we
find it in the higher animals. Now, if we descend through the
scale of animal life, we will find this digestive apparatus be-
coming simpler and simpler, the organs are fewer and fewer
in number. If we take the earth worm, for instance, we will
find simply a straight tube, and very few glands in connection
with that tube. There is one large gland, or apparently a
salivary gland, situated near the mouth, and then a straight
tube, lined with simple columnar epithelium. (Makes draw-
ing on board.) Let that represent the outer skin, if we may
so term it, of the earth worm. We will find it covered all
over with a columnar epithelium. Then within that there is
a layer of muscular tissue, and upon the inner surface a mem-

brane, and within that again we will find another layer of
muscular tissue, forming the alimentary canal, which I have
made with red chalk, which is studded on the inner side with
columnar epithelium, and between the two is an open space
filled with fluid—the peritoneal cavity. Now we have in that
little animal a tolerably extended system of cells which may
be called liver cells ; they are attached to the digestive tube
by a pedicle and float freely in the peritoneal cavity, but each
cell or little gland has its own tube or duct entering into the
alimentary canal, and we will find these in little flask shapes
all around that, with the little tube extending through, and
the contents of the cells are a little bit granular, so that in
watching that carefully we may see the escape of the secre-
tion from those cells into the tubes. And these are the only
glands, except the simple epithelium of the tube, that can be
found in the earth worm. I should have put in here in the
drawing (indicating) the spinal cord, which we will find with
nerves running of¥ in this manner, forming the nervous sys-

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