couldn’t live on this earth unless you had some of every
one of its elements in you.
“Matter is always becoming.
Matter never is anything, but it is always
becoming something else.”
The vast diversity of color in nature, and in living
forms, is a subject of universal wonderment, a delight to
the eye. But
aside from the aesthetic appeal of color, pigmentation also
holds a special interest for the professional in many fields
of activity. Chromatology,
or the study of colors, finds useful application in
medicine, agriculture, and many other arts and industries.
In the field of biochemistry the comparative
metabolism of colored molecules is one of the important
areas of investigation.
In the diagnosis and treatment of disease, the
physician is often aided by visible signs and symptoms
concerning the state of health as reflected by the colors of
tissues and body fluids; and in agriculture, the farmer
quickly recognizes the stages of growth and ripening of his
crops by observing the changing color pigmentation as they
The reason why snow appears white is the same as that
which imparts whiteness to animal structures.
It is the total reflection of light which often
results from the separation of finely-divided structural
materials by air spaces.
The appearance of whiteness may also come from
secretions or deposits in animal tissues which contribute to
the totally scattered reflection.
The color of a chemical compound depends upon the
selective absorption of light within definite wavelengths,
the unabsorbed rays being reflected or transmitted to the
capacity to absorb visible light is due to varying kinds and
degrees of chemical unsaturation in chromospheres
(color-carrying groups) within the molecule.
In fact, the basis of color-manifestation in a
compound is related to modification in the speed or
frequency of motion of one or more pairs of the compound’s
many rapidly-vibrating electrons.
Carotenoids are a group of red, orange or
yellow pigments. These
are present in many plants and creatures, concentrated
particularly in the yolks of eggs, sexual organs, hair,
skin, eyes and milk. Marine
animals derive carotenoids from rich supplies of seaweed or
microscopic underwater plants.
In man, the skin may turn slightly yellow from an
excessive intake of such carotene-rich foods as carrots or
otherwise harmless condition is call artificial jaundice,
and clears up when intake is reduced.
eight, page 2
The bright color of the flamingo, as well as many
fishes and other creatures, is due to some derivative of
carotenoid present in their systems.
Naphthoquinones and Anthraquinones are
pigments less well known, used particularly for dyes.
The former produces yellow, orange, red and purple
pigments, especially from sea animals.
The latter produces various red pigments obtained
from certain insects.
Flavones and Tetrapyrroles:
The flavones impart yellow color to certain flowers
and are found in some insects.
The tetrapyroles are nitrogenous, water-soluble
pigments called porphyrins.
They are found in plant chlorophyll, and in animal
hemoglobins, present in the red blood cells of most
are responsible for the pink to red color of the combs and
wattles of birds, and the skin of man.
Certain underwater creatures fade in aerated water,
but increase in redness when placed in water with a poor
supply of oxygen – apparently a physiological adaptation
Hemoglobin is also present in the bacteria-harboring
root of peas, beans and other leguminous plants.
It is believed to serve as a catalyst for the
chemical fixation of atmospheric nitrogen in the soil, a
well-known property of the root nodules of legumes.
There are many related pigments, some in the blue and
If an apple is cut so that its flesh is exposed to
the air, the surface of the cut begins to turn brown.
The brown color is caused by a pigment called melanin
that is formed by the action of the air on one of the
chemicals that is in the apple.
Melanin is also found in the skin and hair of human
Because of the high frequency, each photon of
ultra-violet light has a high amount of energy.
It can damage the cells in a living body.
So the body needs protection against ultraviolet
melanin in our skins gives us this protection by absorbing
the ultra-violet rays before they can do any harm.
Dark colors evidence the presence of the melanin
pigment, dark feathers, hair or eyes.
Melanin is an end-product of metabolism, formed as a
result of oxidation and polymerization of phenolic
albino animals fail to develop melanin in their tissues.
Urochrome, the principle yellow pigment of urine, is
considered to be a modified melanin.
In certain diseases melanin precursors cause urine to
darken as oxidation occurs on standing.
Melanin can be bleached by such oxidants as hydrogen
peroxide, chlorine, chromate or permanganate.
Peroxide is, of course, sometimes used to bleach hair
to create a blond effect.
The dark hairs of mammals contain a higher trace of
copper than do pale hairs.
If the intake of copper falls well below the minimal
requirement of a fraction of a milligram per day, the new
hairs which emerge are less dark.
Ellipsoidal or spherical microgranules of
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melanin are randomly distributed
with the dried cortical cells of all colors of hair,
imparting varying degrees of hue from light to dark,
depending on the microgranules of melanin which are present.
Human red hair, unlike any other hair from humans or
animal, is unique in its iron-rich pigment.
Red poultry feathers yield a similar substance.
All human skin, except in albinos, contains greater
or lesser amounts of melanin.
In fair-skinned races the corium, or deeply-lying
skin layer, contains but little of the pigment.
But darker races carry heavier dermal deposits,
fortified by numbers of smaller melanocytes in the upper
skin layer, or epidermis.
Exposure to sunlight causes tanning of man’s skin,
with a gradual increase of melanin pigment, which in turn
helps protect underlying tissues from injurious sunrays.
Certain fishes placed in black-lined containers have
been found to increase the melanophores of the skin, while
after transfer to pale containers, they gradually lose it
interesting phenomena has been observed among the fishes, of
rapid darkening of the skin through melanization.
Tasmanian whitebait as it approaches sexual ripeness
develops an increasing number of melanosphores, then after
spawning shows extensive darkened areas of skin.
Like melanins, the indigo compounds are excretory
products of certain animals, but their distribution as
pigmentary compounds is limited.
Unlike the more somber melanins, many indigoids are
red, green, blue or purple.
Indigo occurs in many plants, and has long
been useful as a blue dye.
It does not occur in the tissue of healthy animals
but certain chemical derivatives of it are found in
secretory and excretory products.
Tyrian Purple is called a “dibromindigo”,
and is a purple known to the ancients, the red-violet dye
employed commercially in some countries.
It is a product secreted by several species of snail,
of the genera murex and purpura.
Purines and Pterins:
The purine compounds are hardly true pigments, since
they are usually white crystals, but they often contribute
to the color scheme of some lower animals.
Solid white uric acid is found in the excrements of
birds and other creatures.
Small amounts of uric acid are found in man and apes.
(Gout is partially caused by the deposition of sodium
urate in the joints).
The brilliant whiteness of some anemones results
partly from microcrystalline deposits of uric acid in the
purines occur in the wings of butterflies.
Purine compounds constitute part of the complex
nucleic acids which abound in the nuclear material of all
cells, and therefore play an important part in cell
There are several other related compounds in the
white and yellow range.
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This is a class of yellow, greenly-fluorescent
water-soluble pigments widely distributed in plant and
animal tissues, but in such small amounts as to make no
appreciable color change.
Lyochromes are synthesized by bacteria, yeasts and
green plants. A
very important one of these, called riboflavin, is identical
with vitamin B2.
This is not manufactured by animals, but must be
derived from plant sources.
It is part of an enzyme capable of combining with
molecular oxygen, thus developing a yellow color.
The release of oxygen in intracellular oxidation
processes brings about simultaneous loss of color, which is
restored by fresh supplies of oxygen.
A nutritional lack of riboflavin in the diets of test
animals retarded growth, caused development of cataracts,
and impairment of cellular respiration.
The compound is not stored in quantity.
Milk, eggs, liver, kidney, blood and muscles contain
There are many other animal coloring matters, which
are of lesser importance, or not as yet under-stood, which
we may by-pass at this stage.
Most pigments have roles related to their
light-absorbing or light-reflecting qualities.
In the eyes of some creatures, certain pigments in
the violet range regular the admission of light.
Reflecting pigments cause the night eye-shine of
It is possible that light-absorbing and –reflecting
pigments in the skin may be involved in a primitive
mechanism for temperature regulation in certain cold-blooded
species, for example the desert horned toad.
In the cool of morning its skin is dark, and absorbs
heat rays; as the temperature rises during the day its skin
blanches, thereby reflecting heat rays away from the body.
White in the animal kingdom is sometimes due to
special white substances deposited in the tissues; in other
cases it is due to the lack of colored substances – their
place being taken by air – in the hair of white mammals
and the plumage of white birds, this may be of value in
retarding heat radiation.
It appears that these are given them for protective
coloration, as certain smaller arctic animals who change
their white winter coat for darker fur during the summer.
There are many animals who can change their shade, or
even their actual color, slowly or almost instantaneously,
to conform to their background, and camouflage their
Male birds are usually more brilliant of plumage than
the female. This
again one can suppose is for the protection of the female
during the nesting period when she must melt into the
background, unobserved, sitting on the nest until the babies
have hatched and are safely launched.
Plant colors are predominantly green due to
the prevalence of green chlorophyll in the leaves and stems
of most plants, grasses, and trees.
Chlorophyll, one of the most important pigments in
nature, is capable of channeling the radiant energy of
sunlight into chemical energy usable in the reactions of the
cell through the process called photosynthesis.
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Chemically it is related to
hemoglobin, the “heme” in the red blood pigment, as well
as to the respiratory enzymes called cytochromes.
Chlorophyll absorbs nearly all of the red light that
falls on it. Plants
use the energy of the absorbed light to build sugar
molecules out of water and carbon dioxide.
The light reflected by the chlorophyll in leaves is
that which is left over after the red light has been
kind of light mixture imparts to growing plants their green
In the plant world, the carotenoids are almost
universally present in the yellow to orange-red colorants of
nature, such as in carrots, or marigolds.
Carotene is the raw material from which vitamin A is
made. It is
changed into vitamin A by the action of ultra-violet rays.
When the leaves change color from green to different
shades of yellow and red, this is the result of carotene in
The autumn coloring of leaves is due to the
disappearance of chlorophyll, as it decomposes at the
approach of winter, and the formation of anthocyanins.
Anthocyanin gives both purple-red color to autumn
leaves, and the red-purple appearance to young new growth.
Certain mineral deficiency of plants can be detected
by the formation of red anthocyanin coloration.
The flavonoids include anthocyanin, responsible for
red, blue, mauve, purple and violet colors; and the
anthoxanthins, ranging from colorless to yellow.
The latter is responsible for white flowers, cream or
This is just the threshold of the subject of
pigmentation in nature, but it gives some idea of the vast
possibilities of study and research in this field.