Charles Wesley Hargitt.

Outlines of general biology ; an introductory laboratory manual online

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make drawings showing the cells and the intercellular sub-
stance. Mount a drop of blood from the frog and examine
with the high power, draw the various kinds of cells found
therein. If possible place this latter slide on a warm stage
and note the effect on the white corpuscles. In what ways
do these cartilage and blood cells differ from the other cells
already studied, and in what ways are they similar? Try
especially to determine what represents the cell walls in
the cartilage.

7. From the data obtained in the above studies write a
careful description of the cell as you understand it. Tell
particularly what you have found concerning the cell con-
tents, and their functions.



PROTOPLASM OR LIVING MATTER.

IN the preceding study it was found that the cells were
of various sizes, shapes, and uses. In some were found
such storage stuffs as starch, fats, and mineral substances,
in others, and indeed most, might have been noted a more
or less homogeneous or granular substance which has come
to be known as protoplasm, a substance which Professor
Huxley aptly called "the physical basis of life," since life is
only known to us in association with this physical material.
While a great deal of investigation has been devoted to the
study of protoplasm, its chemical nature and its physical
structure, and while much has been learned along these lines,
still that which is as yet unknown is much greater. An
elementary course w r ould not be the place to undertake a
study of these properties of protoplasm, yet it is not beyond
the scope of even such a course to endeavor to observe some
of its more obvious characteristics, and some of the things
which it does. It will be interesting to study something of
its actual activities, its movements, its behavior under
varying conditions of cold or warmth, and to note perhaps
certain aspects of its structure. Since such study can only
be made with the high power of the microscope it will be
necessary to select living things whose structure is such as
to render them favorable for observation, i. e., those which
are sufficiently transparent to enable one to see through
them and note all that takes place within. Certain plant
cells are especially favorable subjects, as are also some of
the transparent animal organisms, like the common amoeba.



48 GENERAL BIOLOGY

The following types, among others also available, afford
good material for such study.

I. Protoplasmic Movement.

1. Mount some of the healthy, younger leaves of Elodea
in water and with the high power examine their structure.
In the cells look for rather large green bodies, the chlorophyll
bodies. What is their form and how are they arranged in
the cells? These bodies float in a liquid, the protoplasm,
which is so transparent it is exceedingly difficult to see.

Having noticed these features of structure look closely
for any signs of movement in the cell contents. The move-
ment is not rapid nor it is continuous, but you should observe
it in some of the cells of the young leaves. Make a draw-
ing of several cells, showing the chlorophyll bodies, and by
arrows indicate the direction of movement of the -proto-
plasm.

2. Mount a cluster of leaves from the tip of the stem of
the stonewort, Chara or Nitella. The younger, more trans-
parent cells in this cluster should show the circulation of the
protoplasm very clearly. It will be necessary to focus
through the outer layer of the protoplasm w y hich contains
the chlorophyll bodies, the latter being stationary in this
form. Note the direction in which the protoplasm moves,
and whether all the cell contents are involved. Make a
drawing of the cell as seen with the high power, and indicate
by arrows in what direction the protoplasm is moving. It
may be possible to see the nucleus w r hich is carried along by
the currents.

3. In the cultivated spiderwort (Tradescantia) the stream-
ing of protoplasm is beautifully shown. If the flower of
this plant is available take some of the hairs which are



PROTOPLASM OR LIVING MATTER 49

present around the stamens, mount in water and with the
high power observe the protoplasmic movements. Record
your observations in a drawing.

4. If amoeba is at hand observations should be made on
the streaming or flowing movements of the protoplasm.

II. Cib'ary Movement.

In certain cells, particularly of animals, the protoplasm
is extended beyond the free ends of the cells into very del-
icate vibratile filaments called cilia. Mount a small frag-
ment of the gill of a clam, or the cells scraped from the roof
of the frog's mouth, and look for these moving cilia. Possibly
the only sign will be in the currents of water caused by the
movement of the cilia, the latter moving so rapidly they
can scarcely be seen. In a place where the movement is
not so rapid observe the direction in which the cilia move
and whether they change the direction of movement. Make
a drawing.



THE CELL.

CYTOLOGY.

THE unfertilized egg of the starfish is a good example of
a typical cell or egg. Other eggs as those of Cerebratulus,
the large jellyfish Aurelia, or tissue cells, if large, may serve
equally well.

1. Form. Are the cells alike in shape and size? The
shape of a 'cell, if unconfined, is usually spherical, but in
tissues this form is modified by the pressure of adjacent
cells, or as a result of adaptations for some particular function.

2. Structure. The essential elements of every cell are
cell protoplasm or cytoplasm, and nucleus. Is there a mem-
brane about the cell? Note the general appearance of the
cytoplasm. Is it granular, fibrillar, or alveolar? Is the
cytoplasm alike in all parts? In some eggs spheres or
granules of yolk are scattered through the cytoplasm. In
what portion of the cell is the nucleus located? Is this
position constant? Is there a membrane about the nucleus?
What is the character of the contents of the nucleus? If
the cell is stained note the granules, or flakes, within the
nucleus which stain more densely. These are spoken of as
the chromatin, the faintly stained, or unstained, material is
achromatin. Is the chromatin arranged in any definite way
as though on a framework? Within the nucleus is often
a rather large, deeply, staining spot, the nucleolus. Is it
in any constant place in the nucleus?

3. Cell Division. This fundamental feature of living things
presents two rather distinct and definite aspects, namely,



THE CELL 51

mitotic, or indirect division, and amitotic, or direct. The
latter, while apparently simpler, involving the direct di-
vision of nucleus and cytoplasm by a simple pinching into
two parts, is yet less common than the former, and no
attempt will be made to study the process in this connection.

Mitosis. In sections of the root tip of the onion, or of
the testis of the grasshopper, study the cells which are in
the process of division. Find a stage in which the chromatin
of the nucleus is forming a long tangled thread, or else a
series of densely staining bodies. These bodies produced
from the chromatin of the nucleus are called chromosomes.
Find a cell in w^hich the nuclear membrane is disappearing.
What is the position of the chromosomes? Do you find
a spindle made up of delicate fibers to which the chromo-
somes are attached? In the cells of some organisms there
is a tiny spot, the centrosome, at the end of the spindle and
from this centrosome starlike rays, the aster, radiate into
the cytoplasm.

Next examine a stage where the chromosomes are grouped
into a mass, or plate, at the center of the spindle. At about
this stage each chromosome splits into two parts, and the
halves separate and are drawn toward the poles of the spindle.
In this position the chromosomes lose their distinctness,
form a new nucleus with a membrane, the body of the cell
divides into two parts and we have the division of the cell
completed.

The stage of the formation of the chromosomes and their
arrangement in the spindle is called the prophase of divi-
sion; the splitting of the chromosomes makes up the meta-
phase; the separation and the pulling apart of the chromo-
somes comprises the anaphase ; the formation of a new nucleus
and the division of the cell body is the end or telophase.

Make a drawing of a cell in each phase of division.



52 GENERAL BIOLOGY

It should be clearly understood that the nuclear changes
described above constitute an uninterrupted process. The
separation of the process into distinct -phases or stages is
made for convenience in description and analysis. The prep-
arations on the slides which show the distinct phases, there-
fore, represent cells which were killed in the midst of the
process, and which were permanently fixed in this condition.

4. Cleavage and Development. In order that an egg may
develop and grow into a new organism several preparatory
processes are essential. First a ripening or maturation
process is necessary for both the female reproductive cells
(ova or eggs) and the male reproductive cells (spermatozoa).
After maturation fertilization must occur, and this consists
in the union of an ovum and a spermatozoon. The fertilized
egg is now capable of further development which is initiated
by a division into cells, a process called cleavage or segmen-
tation.

In dividing starfish eggs look for stages of 2-, 4-, 8- cells.
Are these cells enclosed within a membrane? Are they of
equal size? Each cell continues to divide until a large
number are present, and these are arranged in the form of
a hollow sphere, the blastula. Are all the cells of the blastula
of the same size? Look for other stages in which one side
of the blastula is flattened or pushed into the hollow of the
sphere. Such a stage is spoken of as the gastmla and is
really a double-walled sac or embryo, the outer wall mak-
ing up the ectoderm and the inner the entoderm. Later a
middle layer or mesoderm, is formed between the ectoderm
and the entoderm. These three layers are the germ layers
of the embryo from which are differentiated the organs of
the developing organism.

Study and draw several stages of cleavage, of the blastula
and gastrula formation.



THE CELL 53

In the development of any animal it may be stated that,
from the outer germ layer, or ectoderm are formed the cover-
ing of the body with its protective structures such as scales,
feathers and the like, the nervous system and the sense
organs. The entoderm or inner germ layer gives rise to the
lining of the digestive tube, the gland cells of liver, pan-
creas and stomach, the lining of lungs and trachea. From
the mesoderm are derived the muscle, bone, connective tissue,
blood, heart and bloodvessels, the kidney, reproductive
organs and their ducts.



AMOEBA

THE PROTEUS ANIMALCULE.

AMCEB.E are among the simplest of living things, they
look like tiny drops of clear jelly usually somewhat
granular within. The amoeba will be almost constantly
moving and changing its shape, whence it gets the name of
"proteus" animalcule. This habit of changing the shape
is one of the surest methods of identifying the animal.

Mount on a slide some of the sediment from the dish sup-
posed to contain amoebae, cover with a cover glass and search
for an amoeba with the low power. If one is not found
wait several minutes and examine again; in this time the
amoeba may have crawled out from the sediment. When
an amoeba is found examine with the high power. Be
careful not to move the slide enough to lose the animal.

I. Morphology.

1. Form. Note the changing shape, and the root-like
prolongations of the body called pseudopodia. Are these
pseudopodia alike? How many are there? Is the number
constant? Can you discover their function? Make a series
of 10 outline drawings (each about an inch long) at intervals
of two or three minutes. By means of arrows indicate the
direction of movement of the protoplasm.

2. Structure. The protoplasm which makes up the sub-
stance of the animal is composed of an inner part called the
entoplasm, and an outer ectoplasm. How are they dis-
tinguished? May these distinctions be traced into the



AMCEBA 55

pseudopodia? Is the boundary between the two parts a
sharp one? Which layer is the more fluid? Is there a
definite membrane about the animal ?

Within the entoplasm may be seen food vacuoles which
are usually rather small and spherical, though they may be
quite large and of irregular shape, depending upon the kind
of food which has been eaten. Do you find what might be
considered as lifeless material such as crystals, oil drops, and
the like? In the entoplasm may also be found the contractile
vacuole, a transparent, spherical body which disappears and
reappears at intervals. Its function appears to be excretory.

Sometimes the nucleus can be seen. This is a circular or
oval, denser body, usually granular in appearance. Does
it occupy a definite and constant position in the amoeba?
If it cannot be seen in the living animal examine one of the
stained and mounted specimens.

Make a drawing about two inches in diameter, fill in, and
label all the details mentioned above.

II. Physiology.

1. Movements. Is motion continuous? Regular? How
is it produced? Is there any definiteness of direction?
Watch the formation of a pseudopodium and describe what
part the ectoplasm and entoplasm play in the process. Are
the currents in the entoplasm at all constant? Where are
they the swiftest, where slowest? Trace on paper the path
that an amoeba has taken in the time under observation.

2. Nutrition. If opportunity oft'ers determine how an
amoeba eats, and how it gets rid of waste matter. From
an examination of the food vacuoles determine, if possible,
what the animal eats. Look especially for diatoms and
desmids and for small protozoa. Is there a definite course



56 GENERAL BIOLOGY

of food particles in the body? Where is the food digested?
How is it distributed ?

3. Sensation. Does the amoeba ever appear to feel an
object against which it presses? Does it avoid obstacles?
Tap the cover with a needle, are there indications that the
animal has the sense of touch? If the slide is placed upon
a warm stage it may be possible to determine whether the
animal responds to temperature. If heated to 40 C. the
amoeba will be killed.

4. Reproduction. Occasionally one meets some of the
stages that the animal undergoes in its life history, such as
encysted specimens and specimens undergoing division.
If any of these stages are found examine them with care
and make drawings of them.

Various kinds, or species, of amoebae may be found which
may differ in number, shape and position of the pseudopodia;
in size and abundance of granules in the entoplasm; and
in the presence of a shell about the animal.



PARAMECIUM.

THE SLIPPER ANIMALCULE.

PARAMECIUM is found in water containing decaying
organic matter, i. e., in infusions of organic matter hence
the name infusoria, the class to which the animal belongs.
In nature Paramecium will be found in almost any ditch
or pond which contains much organic matter. In a jar
containing an infusion of hay the paramecia are usually
found near the surface and often in a ring around the edge
of the dish. Mount a drop of water from this region of the
dish, first placing a thin layer of cotton on the slide to trap
the animals, or a solution of gum to lessen the activity.
Examine with the low power.

I. Morphology.

1. Form. Are there individual differences in size? Can
the animals be seen with the naked eye? In outline the
animal is elliptical or oval, often rather slipper-shaped,
whence comes the name "slipper animalcule." Is the shape
constant under all conditions? Watch one while it is pass-
ing through a narrow space. Is the body rigid or flexible?
Are there definite anterior and posterior ends? If so, how
are they distinguished?

With a piece of clay make a model of the paramecium.
Be careful to get the right proportions and shape.

2. Structure. Along one side of the animal is a groove
which leads to a mouth opening. The most satisfactory



58 GENERAL &IOLOGY

way to observe this groove, the buccal groove, is to watch
the animal as it rotates on the long axis (use the low power).
In the clay model already constructed indicate the position
and shape of this groove.

Examine with the high power. If the movements are
not sufficiently restricted to allow the examination of speci-
mens with the high power, place them in a rather thick
gelatin solution, which will retard their movements. Or one
may try the following scheme: on a slide without cotton place
a drop of the water containing the animals and cover with
the cover glass. With a piece of filter paper applied to the
edge of the cover glass slowly draw some of the water from
under the cover. Continue until the cover begins to touch
the animals and to flatten them slightly. At this point it
will be found that the paramecia do not have room to move
about and, being flattened somewhat, the internal structure
is more evident. The success depends upon the remova
of just the right amount of water. Remember the shape
of the animals under these conditions is considerably dis-
torted, and some of the structures are not normal.

Can you distinguish an ectoplasm and an entoplasm? In
what ways are these like, or unlike, the same parts of amoeba?
In a quiet specimen observe the ectoplasm carefully and
look for a delicate outer layer, the cuticle, which serves as
a cell wall. Fine, hair-like, protoplasmic processes, the
cilia, project from the surface of the body. Are these cilia
present on all parts of the body? Are they of uniform
length? In the deeper part of the ectoplasm are minute
oval sacs called trichocysts, arranged perpendicular to the
surface. Very often they look like short stiff rods rather than
sacs. The contents of these sacs may be forced out beyond
the cilia, or even entirely out of the body, and appear as
rather thick threads in the water. The tangle of threads



PARAMECIUM 59

so produced seems to serve as something of a protection to
Paramecium.

Within the entoplasm are food vacuoles, masses of food
forming little spheres or globules and surrounded by a little
liquid. Are these of the same size? Where in the body
are they most abundant? Do they resemble the food
vacuoles of amreba? Do you find contractile vacuoles?
How many? Where situated? Is the contraction or the
expansion more rapid? Just after the disappearance of
the vacuole look closely for radiating canals in the same
region. If more than one vacuole is present observe whether
they contract and expand together. What is the nature
of the contents of the contractile vacuoles? What function
might they serve?

The nucleus can rarely be seen in the living animal. In
order to render it. visible place a drop of methyl green near
the cover glass and draw it underneath by the -use of filter
paper. When the excess of stain is replaced by clean water,
the nucleus should be visible as a green spot. In what part
of the body is the nucleus? This nucleus is called the
macronucleus and is rather large; by its side is a smaller
nucleus, the micronucleus, which is difficult to demonstrate
except by special means of preparation.

A drawing about four inches long should be made and in
it should be represented all the details of structure mentioned
above. Also make a drawing of an ideal cross section of
the animal through the middle region of the body.

II. Physiology.

1. Movements. In what directions may the animal move?
What are the means of locomotion? Run some powdered
carmine under the cover glass and observe the currents



60 GENERAL BIOLOGY

produced by the action of the cilia. What is the general
direction over the surface of the body? In the mouth
groove?

2. Defense. Run some dilute picric acid under the cover
and observe the trichocysts which are thrown out. In a
drawing show the trichocysts and the cilia.

3. Nutrition. (a) Ingestion of food. Place some para-
mecia on a slide with a small amount of powdered carmine
in water and watch the formation of a food ball in the gullet,
and the way in which it is taken into the body. When it
gets into the body it becomes a food vacuole.

(6) Nature of the Food. Study the contents of the food
vacuoles found naturally in the body and determine, if
possible, what the Paramecium feeds upon, especially
whether it is plant or animal food.

(c) Digestion. Observe the changes in form, size and
amount which take place in the food as it passes through
the body. Are there changes in the food vacuole? What
do they mean?

4. Circulation of the Protoplasm. Watch the food vacuoles,
especially after having added the carmine, and see whether
they change their position in the body. If there is any
movement make an outline drawing and show by arrows
the course of the circulation.

5. Irritability. What reasons are there for believing that
Paramecium is sensitive to external influences? Do they
avoid objects? Do they collide with each other in motion?
Do they tend to collect in masses? Where? Why? Are
they as active at the end of the hour as at the beginning?
Why ? Is the animal sensitive to touch or pressure ?

6. Reproduction. (a) .Fission. This is the usual method of
reproduction and consists in the division of the animal into
two parts. At what part of the body and in what direction



PARAMECIUM 61

is the line of division? Can one speak of "parent" and
"offspring"? Stain the dividing animals with methyl green
and note what changes are taking place in the nucleus.

(6) Conjugation. This is of less common occurrence
and depends in part upon the physiological condition of the
animals. Look for pairs of individuals which are joined
together by the buccal groove. This contact of the animals
is only temporary for they later separate; in the meantime,
however, portions of the nuclei have been exchanged. If
slides with stained specimens showing conjugation are at
hand examine them for the nuclear changes involved. Is
there any distinction of sex in these conjugating individuals?



VORTICELLA.

THE BELL ANIMALCULE.

MOUNT some of the scum from the top of the water in
a jar containing Vorticella, and look for tiny bell shaped
organisms borne on a stalk. They are much smaller than
Paramecium and are usually in groups or colonies. Be
sure that there is plenty of water and that the cover does
not press on the animals and distort them. It will not be
necessary to have a layer of cotton on the slide, since the
animals are fastened to a stalk and will not swim away.

I. Morphology.

1. The Stalk. What is its shape? Its length as com-
pared with its width? Its shape when it is contracted and
when expanded? In the stalk there is present cuticle and
ectoplasm but no entoplasm. The central axis (ectoplasm)
is usually easily seen. Does it run through the exact center
of the stalk? With your highest power study the structure
of this stalk and make a drawing of it, very much magnified,
showing how it is constructed and how it connects with the
body of the animal. Can you give any explanation for the
coiling of the stalk when it contracts?

2. The Body. What is the shape when seen from above?
from the side? When the animal is contracted? when
it is fully expanded? In a fully expanded individual note
the peristome or rounded edge of the bell. Does it extend
completely around the bell? The top of the animal is



VORTICELLA 63

raised in the form of a dome or plate, forming the disk.
Between the peristome and the disk is a gutter-like depres-
sion leading into a deep pit, the vestibule. Is there anything
in Paramecium which corresponds to this vestibule? From
the vestibule the esophagus extends downward. Trace its
direction and determine its shape. In Vorticella where
are the cilia located and how are they arranged?

In the body look for a transparent covering, the cuticle.
Is there ectoplasm and entoplasm as in Amoeba and Para-
mecium? Is the differentiation of these layers as marked
as in the other protozoa studied? Are food vacuoles present?
Are there contractile vacuoles ? How many? Where located?
The nucleus is an elongated horse shoe or "C" shaped mass
in the entoplasm. It may be more easily found if the animals
are stained with methyl green. A micronucleus is present,
but is so small as to be found only with great difficulty.

II. Physiology.

1. General Movements. Observe the manner in which the
stalk contracts. What changes take place in the body
during this contraction? May the body contract without
a contraction of the stalk? Note the rapidity of the move-
ments in the contraction and in the expansion. How does


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Online LibraryCharles Wesley HargittOutlines of general biology ; an introductory laboratory manual → online text (page 3 of 10)