Charles Wesley Hargitt.

Outlines of general biology ; an introductory laboratory manual online

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will be found, and these can be followed for only a short
distance

1. Heart. Observe again the shape and position of the
heart, and the chambers of which it is composed.

2. Arteries. Leading from the ventricle is a single large
artery, the truncus arteriosus, which divides into tvtp parts,
one passing to the right, and the other to the left. Each
of these subdivides into three arteries called the aortic
arches. The most anterior of these is the carotid arch, which
supplies blood to the head. Following this is the systemic
arch which, with its branches, carries blood to the trunk
and appendages. The most posterior of the three arches is
the pulmo-cutaneous which conducts blood from the heart
to the lungs and skin.



32 GENERAL BIOLOGY

From each of these large vessels arise a number of smaller
arteries; their origin should be determined, and. their dis-
tribution carefully followed.

A. Carotid Arch. This arch divides into two arteries:
(a) External carotid or lingual which supplies blood to

the tongue and muscles of the lower jaw.
(6) Internal carotid, which passes around the lower jaw
to the roof of the mouth, the orbit of the eye, and the
brain.

At the junction o these two arteries is a swelling,
the carotid gland.

B. Pulmo-cutaneous Arch. This, the posterior of the
three arches, divides into tw r o arteries :

(a) The pulmonary extends to the lungs, in which it
divides into several smaller vessels.

(6) The cutaneous extends anteriorly to the shoulder
w r here it passes dorsally, and, emerging behind the
ear, is distributed over the skin of the back and side.

C. The middle arch, the systemic, extends dorsally,
passes around the esophagus, and the two sides of
the arch unite into a single vessel, the dorsal aorta,
which proceeds posteriorly along the spinal column.
From each side of the arch several arteries arise.

(a) . The subclavian, a large artery which goes to the
shoulder, w-ill easily be found; it continues into the
arm where it is called the brachial.

(6) The occipito-vertebral arises just anterior to the sub-
clavian, passes dorsally through the body wall and
divides into two arteries. Branches from this artery
may extend into the esophagus.

(c) Laryngeal. Along the systemic arch between the
occipito-vertebral artery and the heart is a small
artery, the laryngeal, which goes to the trachea and
larynx.



THE FROG 33

(rf) Esophageal. This artery arises from the systemic

arch posterior to the subclavian, about half way

between it and the dorsal aorta. As a rule it comes

only from the arch of the left side.
(e) Dorsal Aorta. If the stomach is pulled aside this

artery will be found along the spinal column; it is

formed by the union of the systemic arches of the

right and left sides.

Branching from the dorsal aorta are :

(I) Coeliaco-mesenteric. This large artery extending
to stomach, intestine, pancreas, liver, and spleen
comes from the dorsal aorta just posterior to
the union of the two sides of the systemic arch;
but the blood is derived almost entirely from the
left side of the arch. The coeliac artery supplies
the stomach, the mesenteric the intestine, the
splenic the spleen.

(II) Urino-genital and lumbar arteries arise from the
ventral side of the dorsal aorta in pairs, and
extend to the kidneys, reproductive organs, fat
bodies, and dorsal body wall.

(Ill) Near the extreme posterior end of the dorsal
aorta a small posterior mesenteric artery passes
into the rectum.
(/) Common iliac arteries are formed by the division of

the dorsal aorta; they supply blood to the hind legs.

(J) A short distance from its origin each common
iliac gives off, on the outer side, one or more
epigastric arteries which extend to the ventral
abdominal wall.

(II) Slightly posterior to the epigastric a small artery,
the recto-vesical, comes out on the inner side of
the iliac and supplies blood to the bladder, cloaca,
and pelvic muscles.



34 GENERAL BIOLOGY

(g) The sciatic artery is the continuation of the iliac artery
in the leg. Soon after entering the leg the sciatic
gives off a large branch, the femoral artery, which
supplies blood to the thigh muscles. At the knee
the sciatic divides into two chief branches, the tibial
extending along the front of the leg into the foot, and
the peroneal which passes along the back of the leg
into the calf muscles.

Make a large drawing of the heart and arterial
system, carefully showing the origin and distribution
of the vessels studied.

3. Veins. While the arteries have been under investi-
gation it will have been noticed that there were other vessels,
not injected, running parallel with the arteries. These were
some of the larger veins of the body. The veins make up a
system for the return of the blood to the heart, but their
further study will not be attempted here.

Before leaving the study of the circulatory system one
should see the circulation of blood in a living frog. This
may easily be done by examining with a microscope the
thin web in the foot of an anesthetized animal.

V. Nervous System.

The nervous system consists of three general divisions;
the central, composed of the brain and spinal cord; the
peripheral, which includes the nerves connecting the central
system with sense organs and muscles; the sympathetic, a
series of nerves extending to the internal organs.

1. The Central System. Place the frog dorsal side upper-
most and slit the skin along the median line from the snout
to the anus. Lift up the cut edges and notice the pairs of
delicate thread-like nerves which run through the muscles



THE FROG 35

of the body wall to the skin. Next remove the skin of the
body, the roof of the cranial cavity, the muscles of the back,
and with sharp pointed scissors cut away the arches of the
vertebrae. This will expose the brain and spinal cord which
will be found to be covered with a delicate blackish membrane,
the pia mater. In addition to this inner covering there is
an outer one, the dura mater, which lies close to the skull
and vertebrae, and has been removed with the bone.

The following parts may now be identified, beginning
with the anterior end :

(a) Olfactory Lobes. These are at the extreme anterior
end of the brain. They are not distinct lobes but
are separated by a shallow groove from the rest of
the brain. Are the two lobes separate or fused?
Olfactory nerves pass forward from these lobes to
the nostrils.

(6) Cerebral Hemispheres. Two large ovoid bodies im-
mediately posterior to the olfactory lobes.

(c) Thalamencephalon, a narrow, cylindrical portion
connecting the cerebral hemispheres with the optic
lobes. Upon it, occupying a median position, is
a small body, the pineal gland.

(d) Optic Lobes, posterior to the thalamencephalon.
What is the size and shape of these parts as com-
pared with the cerebral hemispheres?

(e) The Cerebellum is a small transverse fold posterior
to the optic lobes.

(/) Medulla Oblongata, following the cerebellum. In it is
a triangular cavity, the fourth ventricle.

(</) Spinal Cord. The medulla tapers gradually into the
cord without any sharp demarcation. Is the cord
as long as the body? Is it of equal width through-
out its length? If not, in what regions is it widest?



36 GENERAL BIOLOGY

A swelling in the region of the arm would constitute a

brachial enlargement, and one near the legs a sacral

or lumbar enlargement. How does the cord terminate ?

Make a large drawing of the brain and spinal cord from

the dorsal side. Use care in getting the dimensions and

proportions accurate, measuring the parts with a rule if

necessary.

Carefully remove the brain and cord from the body,

place in a watch glass of water, and construct an accurate

drawing of the ventral side of the brain. In addition to

the parts already observed the following should be identified:

(h) Optic Chiasma. Formed by the crossing of the optic

nerves as they leave the optic lobes.
(i) Infundibulum. A small shield-shaped body posterior

to the optic chiasma.

(j) Pituitary Body. This lies in a little pocket of bone in
the floor of the skull. It is usually torn from its
attachment to the infundibulum when the brain is
removed from the cranial cavity.

2. The Sympathetic System. This is best seen by placing
the animal ventral side up, moving the viscera to one side
and looking for a very delicate thread-like nerve, the sym-
pathetic nerve, which runs along one side of the dorsal aorta;
a similar nerve is present in the same position on the other
side. When these are found the organs of the body and the
lower jaw should be removed, but the dorsal aorta left in
place. Place the animal under water and lift the dorsal
aorta to find the sympathetic nerves, their ganglia and con-
nections with the spinal nerves. Observe carefully the
relation of sympathetic and spinal nerves, the position and
number of sympathetic ganglia, and the delicate nerves con-
necting spinal and sympathetic nerves.

A single drawing should be made to show the sympathetic
and peripheral systems.



THE FROG 37

3. The Peripheral System. This is composed of the nerves
which come from the brain and spinal cord; the former are
called cranial nerves, the later spinal nerves. There are ten
pairs of cranial nerves, but on account of their close relation
to the bone of the skull their origin and distribution will not
be worked out. If possible examine a demonstration prep-
aration showing these nerves.

The spinal nerves come out in pairs, and each single nerve

arises from the cord by a dorsal and a ventral root. Since

these roots pass through the bone of the vertebral column

their origin is difficult to determine, but the spinal nerves

themselves may easily be found along the dorsal wall of the

body cavity. Determine how many of these nerves there

are, and trace their course and distribution. Give especial

attention to networks or fusions of nerves called plexuses:

(a) The brachial, in the region of the fore limb. Of how

many nerves is the plexus composed? Is the fusion

of these nerves complete? Trace a large nerve, the

brachial, into the arm.

(6) The sciatic or lumbar plexus, is in the posterior part
of the body anterior to the place where the legs are
attached. Of how many nerves is the plexus com-
posed? What is the nature and the extent of the
union? Trace a large nerve, the sciatic, into the leg.
Follow it in its course through the leg and foot.
Construct a large drawing showing the spinal nerves, and
the sympathetic system so far as it has been studied.

VI. Sections of the Body.

Having studied the organs and the parts of the body
thoroughly, we should have a good idea of the relations of
one part to another. Make a drawing of an ideal cross-

64186



38 GENERAL BIOLOGY

section of the body of the frog showing all the organs and
parts in their proper relation and proportion.

VH. Microscopic Anatomy. (Histology.)

This involves the study of the tissues and cells of which
the various organs are composed. It will be found that
there are only a few kinds of fundamental tissues and these
are repeated over and over again in the various organs. The
relations of shape and position may differ somewhat in
different places, but the tissues have the same general ap-
pearance and function wherever they are found.

1. Tissues.

(a) Blood. Mount a drop of the blood of a frog on a slide,
and cover with a cover glass. Observe the colorless
fluid or plasma in which are floating the corpuscles
or blood cells. How many kinds of cells do you find?
Observe their shape, color, relative size, and compar-
ative numbers. Are the cells nucleated? If the slide
is placed on a warm stage it may be possible to
demonstrate the movement of the white corpuscles.
Draw.

(b) Epithelium. Epithelial tissues are those which cover'
the free surfaces of the body or line cavities. The
outer skin and the lining of the digestive tube are
examples. Epithelium is of different kinds according
to the shape, structure and arrangement of the cells.
(I) Squamous or Scaly. Examine the epidermis of

the frog. What is the form of the cells? Are
nuclei present? Do the cells form a layer? Do
they overlap at the edges? If possible examine
sections made vertically through the entire skin.
In these sections only the outer layers of cells
make up the epithelium. Draw.



THE FROG 39

(II) Columnar. Examine prepared slides which show
sections through the intestine of the frog. What
is the form of the cells lining the cavity? How
are they placed? What is the position of the
nuclei in the cells? Goblet cells, which contain
secretions of mucus, are often found in the
epithelium. Draw.

(Ill) Ciliated. Examine the cells scraped from the
roof of the mouth of a freshly killed frog. Com-
pare the cells with those of squamous and colum-
nar epithelium in all points. In what are they
alike? In what different? Can you see the
movement of the cilia? Where on the cells are
the cilia located? Draw.

(c) Cartilage. Examine prepared slides of cartilage, or
make a slide of fresh cartilage from the frog. Get a
very thin piece and observe the transparent matrix
in which are embedded the cartilage cells. Note
the shape and the size of the cells and the manner in
which they are grouped together. How does the
cartilage differ in appearance from the other tissues?
Are the cells nucleated ? Do you find cells with more
than one nucleus? Explain. To what does the
matrix correspond in the other tissues? Draw.

(d) Muscle.

(I) Striated. The striated (voluntary) muscles are
those that are under the control of the will.
Examine the muscle of the leg of the frog, by
teasing it in salt solution. The fibers should be
well pulled apart. What is the shape of the
fibers? Do they tend to separate into smaller
fibrillae? Is there anything that suggests the
name "striated" muscle? If nuclei are present
where in the fiber are they located? Draw.



40 GENERAL BIOLOGY

(II) Smooth or unstriated muscles. These are muscles
which are automatic in action, or at least not
under conscious control. The muscles of the
intestines, the bladder, etc., are examples. A
piece of muscle from the stomach when teased
should show the fibers. Observe the shape,
arrangement, and nuclei of the fibers. Draw 7 .
(e) Nerve Tissue.

(I) Fibers. Tease the sciatic, or other large nerve,
in salt solution. In a single fiber look for a
place where it is torn or crushed and identify
the delicate sheath on the outside. Inside this
is the thicker medullary sheath. Making up
the center is the axis cylinder, axone, or nerve
proper. Draw.

(II) Cells. Remove one of the spinal ganglia and
tease in a drop of salt solution containing some
stain, or study prepared slides showing the
nerve cells. Look for large cells and note the
relation of the cells to the fibers. Is there a
nucleus in the cell? Draw.

2. Organs. Having studied several of the fundamental
tissues one should be able to recognize them in organs. In
the following study observe what tissues are present and
how they are arranged :

(a) Spinal Cord. In prepared slides of sections of the
spinal cord note the following points: shape, size,
surrounding membrane (pia mater), nerve roots, dorsal
fissure, ventral fissure, central canal, position of the
white matter, shape and position of the gray matter.
In the white matter will be found nerve fibers, con-
nective tissue, bloodvessels and corpuscles. In the
gray matter the nerve cells will be rather prominent.



THE FROG 41

Make an outline drawing four inches in diameter showing
the relative position and proportion of these parts. Arrange
the drawing with the dorsal side of the cord toward the top
of the page. Fill in with care some of the details of structure
observed.

(6) Stomach. With the low power observe the four
layers of the wall, as follows, from without inward:
(I) Serosa or Peritoneum. (This is very delicate

and may be lacking.)
(II) Muscular coat, consisting of

(1) an outer longitudinal layer. Note the
shape of the cells. Do all contain nuclei ?
How do you account for this?

(2) an inner circular layer. What is the
shape of the cells? Are nuclei present?
What is the relative thickness of the two
layers?

(III) Submucosa. Made up chiefly of connective
tissue and bloodvessels. Note the general
character of the tissue and the staining proper-
ties.

(IV) Mucosa or Mucous Membrane. This is marked
off from the submucosa by a narrow band of
muscle cells (the muscularis mucosae). The sur-
face is covered with columnar epithelium which
dips down to form numerous pits into which the
gastric glands empty. The glands are sur-
rounded by connective tissue.

Make a drawing three inches in diameter of a segment
of the stomach wall as seen under low power.

Under high power study a portion of the mucosa and note
the following points: shape of the gastric glands; general
character of the epithelium lining the pits, the shape of the
cells and the position of the nuclei.



42 GENERAL BIOLOGY

Make a drawing of a gastric pit and of the glands empty-
ing into it, as seen with the high power.

Vm. Embryology.

It will be found necessary to have a complete series of
eggs and tadpoles preserved in formalin, especially in large
classes. It is also desirable to have the living material at
hand when undertaking this study.

1. The Egg. Examine the eggs in a mass, also compare
the masses of the toad and other amphibia. How thick is
the surrounding jelly? Distinguish in it three layers, w T ith
concentric layers in them. What is the color of the egg?
The darker side of the egg is the animal or protoplasmic pole,
the side opposite is the yolk or vegetative pole.

Make a drawing of the egg and its envelopes, also draw
each of the following stages as studied.

2. Early Cleavage Stages. What evidence do you find
that the egg differs from the ones previously studied? Find
one with a single groove surrounding it. In what direction
does the groove extend? Are the resulting parts equal?
Find an egg with a second groove at right angles to the first.
The first one gives the two-cell stage, the second one the
four-cell stage. Are the cells equal in size? The third
groove passes in a horizontal or equatorial direction. How
many cells result ? What is their relative size ?

3. Later Cleavage Stages. Study eggs in the sixteen-cell,
and thirty two-cell stages. How are these stages produced
from the earlier stages? Are the cells equal in size? Ex-
amine both poles of the eggs and explain the differences
found. Does the relative size of the pigmented and un-
pigmented areas remain unchanged in later cleavage stages?
How is this to be explained?



THE FROG 43

4. Blastopore. The pigmented cells divide more rapidly
than the white cells and come to grow over the latter; at
the same time the pigmented cells become infolded and grow
into the egg itself. This continues until but a small mass of
white cells can be seen. The term blastopore is applied to
the opening, and the mass of white cells is spoken of as the
yolk plug. Later the blastopore closes and the yolk plug
is forced inside the egg.

5. Neural Groove. On what is to become the dorsal side
of the body will be found an open groove with slightly
elevated margins. How far does it extend? Is. it open
throughout its length? Examine several specimens. What
distinguishes the part which is to form the brain from that
which will produce the spinal cord? The margins grow
together to form a tube and this subsequently develops into
the brain and spinal cord. How does the shape of the
embryo compare with the earlier stages? In eggs which
have elongated, is there any marked difference between
dorsal and ventral, anterior and posterior?

6. Gill Stage. In a tadpole just hatched observe the be-
ginning of the formation of head, body and tail. There is no
mouth yet present, but on the ventral side of the head are
suckers by which the tadpole adheres temporarily to some
support. Nostrils and eyes are beginning to form, and gill
buds indicate the position of future gills. In a somewhat
later stage finger-like gills are produced upon the sides of
the head. At such a period mouth, eyes, nostrils and tail
are well formed, and the internal organs are undergoing
their development.

7. Tadpole. Distinguish head, body and tail regions.
What has become of the external gills? The fold of skin
covering the internal gills is the operculum and the opening
to the gill chamber is the spiracle. On which side is the



44 GENERAL BIOLOGY

spiracle found? At this stage the eye, mouth, nostrils and
teeth are well developed. Also on the ventral surface the
heart, internal gills, and coiled intestine will show through
the body wall.

8. Metamorphosis. The tadpole or fish-like stage con-
tinues for some time (it may be a year or two in frogs) be-
fore a metamorphosis into the adult form begins. This
metamorphosis is first shown by the formation of the hind
legs. Carefully study a tadpole with the hind legs present
and determine the character of sense organs and other ex-
ternal features. The forelegs start their formation within
the gill chamber and are not apparent externally until
they become rather large, when they break through the
skin covering the gills. In a specimen with both fore and
hind legs observe the changes in form of the body and head.
As the legs increase in size what becomes of the tail?

Dissect the ventral body wall from a large tadpole with-
out legs, and also from one with both pairs of legs present.
Determine what changes are taking place in the internal
organs during this time. When the tail is finally absorbed
and the toad or frog leaves the water, the animals are like
adults except for the reproductive organs, which require
a considerable time for their perfect development.



ORGANS, TISSUES AND CELLS.

THE term organism, as used in biology, designates in
general an individual animal or plant, and implies that they
are composed of organs. For example, the ears, eyes, legs
feet, of a dog are familiarly known as organs; and the same
is true of such internal structures as stomach and liver. It
is perhaps not so well known that organs are likewise
complex structures made up of simpler components, and
as in general these are composed of a network of similar
elements they are usually spoken of as tissues. To demon-
strate the organic structure of a frog it is only necessary to
critically observe its external features, or perhaps dissect
and lay open its interior. To demonstrate that organs are
composed of tissues will require the use of the microscope,
and in most cases some means of dissecting and preparing
them for study. This phase of biology is known as micro-
scopic anatomy, or histology. Finally, such a study will
reveal the fact that a given tissue is composed of still more
elemental .structures which are called cells. The following
outline of laboratory study will afford a direct introduction
to these phases of our subject.

1. Mount in water a small fragment of frog epidermis,
and examine with the high power. Make a careful drawing
of a group of cells, showing cell walls, and nuclei.

2. Strip the epidermis from the upper surface of the leaf
of Tradescantia, mount in water and examine. Compare
the shape, size, and general appearance of the cells with
those of the animal epidermis. Make a drawing of a group
of cells.

3. With a razor cut very thin transverse and longitudinal



46 GENERAL BIOLOGY

sections of the stem of Tradescantia, of geranium, begonia,
or other plants, mount these in water and examine. In the
cells near the center of the stem note the shape, arrange-
ment, and cell contents. Look especially for crystals in
these cells. The presence of crystals in the cells indicates
the presence of what kind of material?

4. Cut very thin sections of a potato tuber just beneath
the skin. Mount in water, study and make drawings of
the cells and their contents. Remove the cover glass, add
a drop of dilute iodine solution and allow it to remain for a
few minutes. Wash off the iodine, replace the cover glass
and examine the section again. Since the iodine solution
has the property of turning starch blue what do you con-
clude as to the cell contents in this case?

5. Stems of other plants may be sectioned and treated
in the same manner, and an idea obtained as to the abun-
dance of starch and its position in the plant. What is the
use of this starch? What explanation can you give as to
the differing amounts of starch and of the different places
of storing it in the plants examined?

6. Examine cartilage from a frog or other animal and


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