energy it is said to have kinetic energy.
It is essential to determine the heat value of various
foods, in other words, to find out how much heat and
energy will be derived from the different foods after
their ingestion and digestion, etc. This may be deter-
mined experimentally by the use of an instrument
known as a bomb calorimeter, the result being expressed
in calories. A calorie is the amount of heat that is
necessary to raise the temperature of 1 kilogram of
water 1 C. (It is nearly equal to the amount required
to raise one pound of water 4 Fahrenheit.) This
expressed in mechanical force, means that a calorie
would raise a ton about 1.54 feet, or that it is equal
to 1.54 foot-tons.
The number of calories required to furnish heat and
energy sufficient to accomplish a certain amount of
activity varies, depending upon the age, sex, amount
of work, mental and physical, and climatic conditions.
It is essential to know how many calories are required
to perform a certain amount of work from the taking
of various foods into the body, to make a proper appli-
cation of dietetics in the feeding of healthy and diseased
> with the
Nuclear fluid -
Diagram of a cell. The lower segment illustrates the fibrillar theory, the
upper the granular theory, the left the foam theory. At the right the proto-
plasmic threads radiate from the centrosome. The nuclear network consists
of nuclein, linin, and lantanin. (Symonowicz.)
The cell, protoplasm or bioplasm is the anatomic
and physiologic bases of the body. All growth, repair,
disintegration, heat, energy, and life of the tissues
(whether normal or abnormal) depend upon the histo-
logic cell as a unit to work upon. Cells are seen only
32 THE CELL, ITS STRUCTURE AND FUNCTIONS
microscopically. They vary in size and may measure
from ^ViT of an inch, the diameter of a red blood cell,
to Y-J-tf of an inch the diameter of the large cells in
the gray matter of the spinal cord. The structure of
a cell consists of a gelatinous substance, usually homo-
geneous, called protoplasm or cytoplasm, containing
a small spheric body, the nucleus, which latter con-
tains the nucleolus. Young cells appear clean, mature
cells contain, depending on the tissue they are found
in, different substances, e. g., fat-globules, granules of
glycogen, mucigen, pigments, and digestive ferments.
Cells possess the power of changing their shape, and
are also capable of growth, nutrition, and reproduction.
Growth. Newly reproduced cells are very small,
but they soon grow, owing to their characteristic
organization and surrounding medium, to resemble
the normal adult cell of a given tissue.
Nutrition. Cells not only must grow, but they have
to repair or make up the loss from waste, etc. Growth
and nutrition are dependent not only upon the power
possessed by living material of absorbing its nutrition
from the lymph, but also upon the property of taking
that nutrition and converting it into material similar
to its own, before waste took place, and then endow-
ing it with physiologic functions. Thus we have a
cell doing work, wasting as a result of such labor;
repairing not only its own body, but renewing its
powers of doing fresh work.
Reproduction. Cells reproduce themselves by two
methods, direct and indirect division. (See Figs. 2 to
16, pages 36 to 39.)
Direct division is seen when the nucleus of cells
becomes narrowed and divides with a grouping of the
nuclear elements. This is believed to occur only
where cell disintegration occurs. Indirect division
this is called karyokinesis is a complex process and
its main feature is due to the centrosome of a cell
becoming enlarged and in leaving the nucleus lying
THE CELL 33
in the surrounding protoplasm. The chromatin
becomes contracted and is seen as V-shaped loops
(chromosome), with thin closed ends pointed toward
the common centre, the polar field. The mother
stars are formed, which rapidly give origin to daughter
stars, in which the chromatin can be seen as two
separate nuclei grouped in a single mass of protoplasm;
at this stage the protoplasm becomes constricted
and two separate cells are seen lying in their own
protoplasm. (See Figs. 2 to 8, pages 36 and 37.)
Cells of the animal and human body, or in fact all
living protoplasms, possess the properties of irritability,
conductivity, and motility.
Irritability or the power of responding to some exter-
nal excitant. This can be mechanic, chemic, or electric ;
thus if the protoplasm acted upon be muscle, it will
contract; if a gland, such as the parotid, saliva will
be secreted; if a nerve, a sensation, as when we apply
heat, cold, etc., to the skin; or other nerve activity,
as seen in the contraction of the pupil when one looks
suddenly at a bright light. It must be remembered
that the degree of the response in the foregoing depends
upon the protoplasm acted upon and the nature and
strength of the irritating principle.
Conductivity is developed best in muscle and nerves,
as seen when molecular disturbances occur at the ex-
tremity of the peripheral nerves, and are conducted
to the brain, and the same phenomena arising in the
brain are transmitted to the peripheral nerves.
Motility is the power possessed by cells of apparent
active movement in response to natural causes, which
scientists have not yet determined. This motility is
best seen by microscopic technique and observed in the
ameboid movements of the white cells of the blood,
the waving of cilia, the activities of the spermatozoons
and ova during impregnation, or the commencement
of pregnancy, etc.
34 THE CELL, ITS STRUCTURE AND FUNCTIONS
1. Describe the term metabolism.
2. Is oxygen considered a food?
3. What do you understand by the term katabolism? Anabo-
4. Why is food essential to the body's requirements?
5. What is meant by a calorie?
6. What term is used that expresses the determination of the
amount of heat and energy to be derived from the different foods
we eat and digest?
7. What factors will vary the determination of the number of
calories required to furnish a certain amount of heat and energy
from the food we eat?
8. What histologic unit underlies all the phenomena of physio-
logic life as: growth, repair, disintegration, heat, energy, and life
of the tissues?
9. What functions is a cell capable of?
10. How do cells derive their nutrition? Repair waste? Renew its
11. How do cells reproduce themselves?
12. Describe the term karyokinesis.
13. Name the properties of a cell.
14. What external stimulus will produce irritability in a cell?
15. What do you understand by the term as used in connection
with the properties of a cell-irritability? Conductivity? Motility?
To grasp an understanding of the various tissues
properly, a brief description of the cells from which
they are developed, embryologically, will be necessary.
The Ovum. The ovary secretes a cell, the original
cell of the female human body, called the ovum. The
ovum consists of a limiting wall, the vitelline membrane,
enclosing the protoplasm, vitellus, which consists of
two parts the dentoplasm or nutritive yolk, and the
animal protoplasm or formative yolk. Within the
vitellus is found the nucleus or germinal vesicle, which
contains the nucleolus or germinal spot.
Before an ovum can develop into an offspring it
must undergo numerous complex changes. The two
most important phenomena are defined as maturation
Maturation. Maturation or ripening is the process
taking place in the ovum, which prepares it for the
reception of the male element spermatazoon, where
its contained chromatin and a small part of the proto-
plasm are collected into the form of two minute
structures called polar bodies, when a modified cell
reproduction or karyokinesis occurs. This reproduc-
tion must take place before ova can be fertilized.
Fertilization. This is the process in which the male
and female units the ovum and spermatozoon unite
to form a complete and perfect cell, by division,
which ultimately develops into cells which form the
tissues of the whole body.
The male element or spermatozoon or spermium con-
sists of a head, middle-piece, and tail. After entering
FIG. 2 Fin 3
Diagrams illustrating cell division karyokinesis.
THE OVUM 37
FIG. 7 Fid. 8
Semidiagrammatic representation of the processes of cell and nuclear division
(karyokinesis) in Ascaris megalocephala. (After Kostanecki.)
FIG. 2. Resting cell.
FIG. 3. Division of centrosome.
FIG. 4. Prophase centrosomes at the 'poles; radiation well-developed;
chromatin net-work broken up into four chromosomes.
FIG. 5. Mother-star stage (monaster); chromosomes arranged at the
FIG. 6. Metaphase; the longitudinally divided chromatin filaments moving
toward the poles.
FIG. 7. Anaphase; beginning of division of cell body.
FIG. 8. Division of cell body almost completed; the central spindle shows
the beginning of the intermediate bodies.
the ovum the head and middle-piece, representing
the nucleus and centrosome, respectively, of a cell
from the testicle (the male organ, the cells of which
secrete the spermatozoon) form eight chromosomes.
The chromatin of the germinal vesicle of the ovum
also forms eight chromosomes. The process continues
within the cell until thirty-two chromosomes are de-
veloped by longitudinal cleavage; these are subdivided
into sixteen chromosomes, which enter each diaster or
Stages in the fertilization of Physa fontinalis.
(After Kostanecki and
Fia. 9. Mother-star stage passing into metakinesis for the formation of
the first polar body. The spermatozoon is enclosed in the egg in toto.
FIG. 10. Formation of first polar body; centrosome divided.
FIG. 11. First polar body formed. Monaster stage for the formation of
the second polar body. Sperm radiation is separated from the sperm nucleus.
FIG. 12. Formation of the second polar body. Sperm radiation with two
centrosomes near the vesicular sperm nucleus.
FIG, 43 FIG. 14
/ R K
II RK II RK-;'
FIG. 13. Two polar bodies above. Egg nucleus has become vesicular.
Sperm radiation has increased in size.
FIG. 14. Egg and sperm nuclei approach one another. The sperm radia-
tion and the centrosomes move apart.
FIG. 15. Egg and sperm nuclei closely approximated. The centrosomes
arrange themselves on opposite sides.
FIG. 16. The chromosomes of the egg and sperm nuclei form a monaster
stage to give rise to two new cells.
CSpK, central spindle; EiK, egg nucleus; IFSp, first spindle after fertiliza-
tion; G, tail of spermatozoon; IRK, first polar body; II RK, second polar
body; IRSp, first polar spindle; IIRSp, second polar spindle; SpC, centro-
some of spermatozoon; SpK, sperm nucleus; SpSt, sperm radiation.
After fertilization the ovum divides and redivides
into numerous cells, forming an irregular mass termed
the mulberry mass or morula. The latter collection of
cells divides again into an outer and inner cell mass
called the blastula. The outer mass is supposed to dis-
appear, while the inner continues to develop and forms
two layers an outer, the ectoderm or epiblast, and an
inner, the entoderm or hypoblast. This is termed the
gastrula or diploblast. A third layer is developed from
the two former layers, each setting aside a few cells
which develop the third layer, termed the mesoderm
or mesoblast, that lies between the two layers. The
formation receives the name of blastodermic- vesicle or
All tissues of the body are composed of cells arising
from the cells in the original three layers of the triplo-
blast or blastodermic vesicle. Tissues, which are always
studied microscopically, consist of cells held together
by an intercellular cement, and perform a definite
function; thus they may be supportive, as bone, etc.,
or functional, as the liver, etc. All the tissues to be
seen and understood in their minute arrangement are
first treated by histologic methods in the laboratory
by hardening, sectioning, fixing, dehydrating, staining,
etc., and are then observed under the microscope.
This process is not essential to the nurse's knowledge,
but should she desire a complete understanding of
the subject she should refer to the standard works on
Tissues are divided into epithelial, connective,
muscle, and nerve
Epithelial Tissue or Epithelium. They may be pro-
tective, as the cells of the skin and conjunctiva of the
eye; secretive, as the cells of the pancreas, parotid
gland, etc.; excretive, as the cells of the kidneys;
to prevent friction, as those seen in the cells of the
synovial sacs between the articulating cartilages of
joints, peritoneum, and layers of pleura. Epithelial
SQUAMOUS CELLS 41
cells line cavities that normally communicate with
the air;' except the pleural, peritoneal, and synovial
sacs, and between the articulating cartilages of joints.
Epithelial cells are classified usually as: (1) squa-
mous, simple and stratified; (2) columnar, simple, modi-
fied, and stratified; (3) ciliated, simple and stratified;
(4) prickle cells; (5) goblet cells; (6) transitional cells;
(7) pigment; (8) neuro-epithelial ; (9) glandular.
Flat epithelial cells isolated from the oral mucous membrane of man. X 375
1. Squamous Cells. (a) Simple squamous cells con-
sist of a single layer of flattened elements, each con-
taining a nucleus, usually situated in the centre and
oval in form. They are found in the alveoli of the
lungs, ventricle of brain, descending limb of Henle's
loop in the kidney, and Bowman's capsule of kidney.
(6) The stratified squamous cells consist of layers
of cells one on top of the other. The lowest layer,
the germinal stratum, is arranged in columns, those
above being polygonal. As the surface is reached
the cells become more flattened, forming the squames
or scales. These cells are usually found when they
afford the most protection, as the skin (epidermis)
lining the mouth cavity, pharynx, esophagus, epiglottis,
vocal cords, and the anus and vagina.
Diagram of flat epithelium. I, seen from above; II, seen from the side
after transverse section on the line m. (a) cell boundaries as straight lines;
(6) cell boundaries as wavy lines. (Szymonowicz.)
Diagrams of epithelium: a, nuclei at various levels; b, stratified pave-
ment epithelium; c, stratified cylindrical epithelium, ciliated at the right.
2. Columnar Cells. (a) Simple columnar cells are
arranged in tall columns consisting of a single layer with
a nucleus situated at the base of each cell. They are
found in the stomach and intestinal tract, anterior
portion of the male urethra, glands of Cowper and
Bartholin, prostate, gall-bladder, seminal vesicles, and
many gland ducts. Low columnar cells are often
GOBLET CELLS 43
(b) Modified or pseudostratified cells are simple
columnar or ciliated cells in which the nuclei are at
different levels, thus giving the appearance of several
layers of cells. These cells are found as ciliated
elements in the oviduct, uterus, and middle ear, and
as non-ciliated elements in the seminal vesicles and
(c) Stratified columnar cells consist of numerous
layers of cells arranged one upon another. They are
found in the lining membrane of the vas deferens
(male), membranous urethra, and ducts of some glands.
3. Ciliated Cells. (a) Simple ciliated cells are ar-
ranged in a single layer of columnar cells which have
upon their exposed surface fine cilia or hair-like pro-
cesses; they possess motion that is always directed
toward the outlet of the organ in which they are
located. They are found in the smaller bronchioles,
spinal canal, accessory spaces of the nasal cavities,
and the ventricles of the brain.
(b) Stratified ciliated cells are the same as the
stratified columnar, with the cilia attached only to
the cells of the exposed layer. These cells are found
in the epididymis (male), first portion of the vas
deferens (male), Eustachian tube,
upper part of the pharynx, larynx, FlG - 20
trachea, and nasal tract.
4. Prickle Cells. These are
polygonal elements that possess
little spines, which project from
the sides of the cells, and pass
to meet spines of other cells, thus
preventing the cells from meeting,
at the same time forming inter- prickle ceils.
cellular bridges or spaces. They
are found in the epidermis (skin) just above the genetic
5. Goblet Cells. These are cells resembling the
cylindric type, distended with a secretion called
mucin. On filling they resemble a goblet. When
the secretion has been discharged these cells become
long and slender, the part containing the nucleus
extending on either side. They are found in the
gastro-intestinal and respiratory tracts.
nut tie by
Two ciliated cells and two goblet cells isolated from the frog's esophagus.
6. Transitional Cells. These are stratified cells be-
longing to neither the squamous or columnar groups.
They are polygonal; found in the pelvis of the ureter,
in the ureter, bladder, the first part of the male and
almost the entire length of the female urethra.
7. Pigmented Cells. These are polygonal or colum-
nar in shape, the protoplasm containing pigment.
They are found in the epidermis of the colored races,
and around the nipple and genitals of the Caucasians,
as polygonal cells, and in the retina of the eye where
they assume the columnar shape.
8. Neuro-epithelial Cells. These are cells which have
become so differentiated as to perform a special sense
function. These are found in the retina of the eye, in
the internal ear (hair cells), in the olfactory mucous
membrane*, in the taste-buds of the tongue, and tactile
cells in the epidermis.
9. Glandular Cells. These are found in the pancreas,
liver, etc., and their shape varies according to the
gland in which they are found.
Mucous Membranes. All the surfaces of the gastro-
intestinal and pulmonary tracts, genito-urinary appar-
atus, etc., within the body are covered by epithelial
cells, called mucous membranes, These membranes
are protected in the various organs by a superficial
layer of cells their variety depending on the tissue
they are found in which we have described above.
Beneath this layer the cells rest upon a delicate base-
ment membrane, the next layer is the tunica propria
consisting of a layer of fibro-elastic tissue. Within
this layer are lodged the capillary bloodvessels,
nerves, lymphatic spaces or channels, and, in certain
organs, glands and lymphoid tissue. These thin layers,
are seen resting on a fourth peripheral layer, called
the muscularis mucosse, consisting of involuntary
(not under the control of the will), non-striated muscle
tissue. This layer is sometimes wanting in some tissues.
The above mucous membranes line cavities which
communicate with the air. Their cells usually secrete
a substance called mucin.
Glands. Glands are considered under the classifica-
tion of epithelial tissues. They are simply various
shaped pouches or tubes of mucous membranes grow-
ing out from the superficial surface of the tissue in
which they are located. All glands are lined with
epithelial cells arranged in different groups, and
possessing a physiologic function. These groups of
cells are the units from which the organs develop
Glands are subdivided into (1) tubular, simple,
branched, coiled, compound; (2) tubulo-alveolar ; (3)
alveolar, or racemose glands, simple and compound.
These different shaped glands are lined by epithelial
cells, depending on the situation and function. Their
secretions are liquid, and may be serous, mucous, or
mixed, which the lining cells secrete as needed by the
organ to perform its physiologic function.
Diagram of various forms of glands; a, duct; x, simple tubule; xx, simple
alveolus. (After Szymonowicz.)
Serous Membranes. They are membranes covered
by a single layer of flattened cells, with a large pro-
jecting nucleus; these cells are held together by a
intercellular cement. They are termed endothelial
cells. Serous membranes never have a basement
membrane and line cavities that do not communicate
with the air. These membranes appear smooth,
glistening, and transparent. Openings called stomata
are said to be present between the cells, but they are
supposed to be artefacts according to the latest teach-
ing. Serous membranes line joint-cavities, bursse,
tendon sheaths, circulatory and lymphatic systems,
and the pleural, pericardial, and peritoneal cavities.
White fibrous tissue. (Gerrish.)
Yellow fibrous tissue.
Connective Tissues. The connective tissues of the
body are the elements entering into the formation
of the more permanent structures of the body, such
as bones, cartilages, ligaments, those holding fat in
position, those used as' coverings for muscles as
fascia, as sheaths for bloodvessels, and nerves, as
supports for cells of glands and organs, and those
binding membranes to underlying organs, as the
pleura and peritoneum to the lungs and abdominal
organs respectively. The connective tissues are derived
from the mesoderm.
They are classified as follows: (1) fibrous; (a) loose,
(b) dense; (2) yellow elastic; (3) mucous; (4) retiform;
(5) mixed or areolar; (6) adipose or fatty; (7)
lymphoid; (8) cartilage; (9) bone; (10) dentin (teeth);
1. Fibrous Tissue. (a) The loose variety consists of
fine thread-like fibers held in bundles by a small
quantity of cement substance, and scattered through-
out those groups of fibrils are seen a few cells. This
variety is mostly for the support of capillary blood-
vessels, the capsules of organs, and as a suppurative
element in the tunica propria and submucosa in the
mucous membrane of the respiratory and alimentary
(6) The dense variety differs from the former in
the fibrils being thicker and the bundles larger. The
dense is best seen in tendons of muscles, when it occurs
as parallel bundles. Seen under the microscope on
a cross-section the whole structure is seen surrounded
by a loose sheath of fibers, the epitendineum, from which
septa are seen passing into and dividing it into dis-
tinct or separate bundles of fibers, the peritendineum.
The tendon cells are seen arranged in rows lying
between the individual bundles of fibers.
White fibrous tissue is very strong, inelastic, is
pearly white in color, as seen when the skin is removed
and dissections made of ligaments and tendons. It
serves as a stocking-like covering to muscles, where
it is termed fascia; and is seen as a bluish-white mem-
brane reinforcing muscles and strengthening their
insertions to bones, particularly in the region of joints,
called an aponeurosis.
2. Yellow Elastic Tissue. This, as the name implies,
possesses elasticity; the fibrils are coarser than the
white variety. It is found in the ligamentum nuchse,
which extends from the occipital bone to the spinous
processes of the cervical vertebra, along the vertebral
column, where it is reinforced by white fibrous tissue,
also in the ligamentum subflava, in the vertebral
column, in bloodvessels, and in the skin.
3. Mucous or Embryonic Tissue. This is found in
the umbilical cord of the fetus. It is at first homo-
geneous, then later fibers both white and elastic develop,
the former in bundles, the latter generally single.
Among these fibers are a few scattered, mostly spindle-
shaped, some stellate, and some round cells.
Areolar tissue, composed of bundles of white fibrous tissue and branched
strands of yellow fibrous tissue loosely intertwined. (Gerrish.)
4. Retiform or Reticulum Tissue. This forms the
frame-work of glands and gland-like organs. The