Transparent specimens often appear remarkably different when they are comparatively observed under positive and negative phase contrast illumination. In positive phase contrast, specimen intensity is manifested by relatively medium to dark gray features, surrounded by a bright halo, and superimposed on a lighter gray background. Alternatively, in negative phase contrast, the specimen often appears much brighter on a dark gray background and the accompanying halos are also dark (much darker than the background). This digital image gallery compares identical viewfields of a wide variety of specimens illuminated with both positive and negative phase contrast.

Arrowroot (Maranta arundinacea) Starch Granules - Use of arrowroot plant starch is a long-standing English tradition. Spice purveyors as far back as the 1700s understood the benefits of arrowroot starch and fought over rights to the crops. Since true arrowroot, known formally as Maranta arundinacea, is cultivated only in St. Vincent, there often was not enough product to meet demand. Even today, attaining true arrowroot starch is somewhat difficult. Products often labeled arrowroot are usually a less expensive version of a similar root, which originates in Brazil or China.

Asbestos Fibers - Should it stay or should it go? This controversial question regarding asbestos and its removal has no clear-cut answer and is the subject of great debate. Asbestos is the generic name for six naturally occurring mineral fibers, which have been commonly used in various building materials as insulation and as a fire-retardant.

Blue Mold (Peronospora tabacina) Fungus - The blue mold fungus produces spores that are the result of both sexual and vegetative reproduction. Resting spores, or oospores, are produced through sexual reproduction and are believed to be involved with long-term survival of the species. Sporangiospores are produced vegetatively as the mold, in essence, makes clones of itself. Sporangiospores can develop by the millions within hours after a tobacco plant is infected, intensifying the need for quick action by farmers who want to save their crops.

Budding Hydra - In Greek mythology, the Hydra was a many headed water serpent with deadly breath. The second task of Hercules was to kill this beast, a difficult feat since each time one head was chopped off two more grew in its place. Although hydras, which belong to the phylum Coelenterata, are not quite so dreadful, their appearance and reproductive ability are reminiscent of the mythological creature of the same name.

Chinese Hamster Ovary Cell Culture - Commonly, hamsters are thought of as cute, furry, and disposable pets, but the small, rat-like, Chinese hamster serves a totally different function. These rodents are fairly uncommon as pets because they can be difficult to breed. Ironically, the cells of their reproductive organs are what make them so useful to scientists. The Chinese hamster ovary (often abbreviated CHO) tissue is commonly cultured as individual cells in a monolayer and studied worldwide.

Ctenoid Fish Scale - The fish most people encounter today are deep-fried, square-shaped and surrounded by a bun. It is almost possible to forget that fish begin their lives covered in scales, rather than a crispy batter shell. Yet, scales are an essential part of fish anatomy, providing these aquatic creatures with external protection from many predators and dangers, if not from man.

Dacron Polyester Fibers - Polyesters may be most memorable as the material used to make sleek and shiny disco clothes during the seventies. Polyester fiber does, however, have more practical uses and may be found in a variety of domestic products, such as mattresses, pillows, seat cushions and custom upholstery.

Earthworm Nervous System - Earthworms are simultaneous hermaphrodites, with each worm having complete male and female reproductive systems. Although earthworms possess ovaries and testes, they have a protective mechanism against self fertilization and can only function as a single sex at one time. Therefore, they still need to mate with another worm in order to produce offspring. Young earthworms are faithful, but miniature, replicas of the parents and become sexually mature in about three months.

Frog Blood Cells - Unlike typical mammalian red blood cells, those from amphibians, such as frogs, contain a DNA-bearing nucleus that is visible in the center of the cell. The circulatory system of amphibians is rather unusual, their hearts having three chambers, two atria, and a single ventricle.

Fucus Seaweed - Members of this small genus of seaweeds are often seen washed up on the shores of beaches. Commonly called wracks, Fucus has a brown mossy appearance and a typical salty sea-like smell. Some species may have health benefits, which although not scientifically proven, are frequently advertised as key components in nutritional supplements.

Goniatitic Cephalopod Fossil - Goniatites are an extinct species of ancient marine animal that evolved approximately 400 million years ago. Flourishing in the Devonian period, goniatites now act as important zone, or index, fossils to geologists who use them to identify rocks of that period. All knowledge concerning goniatites derives from fossil records and familiarity with their modern-day relatives.

Hemp Fibers - Today, hemp products are surrounded in controversy, but as far back as ten thousand years ago they were considered a staple of civilization. Early American colonists were legally bound to grow hemp, and the United States government subsidized the production of hemp during the Second World War. Hemp is a particularly valuable commodity because it is the world's strongest natural fiber.

Honeybee Wings - On warm days in early summer, while others are relaxing, honeybees are hard at work. This species (Apis mellifera) is especially adapted for its primary activity of collecting pollen and participates in a ritual that is perhaps the most famous and fascinating of all the forms of animal communication.

Horsefly Cornea - Horsefly is the common name for many of the stout flies in the family Tabanidae. The bite of adult female horseflies is an annoyance to humans, but an even greater menace to livestock. Adult males survive solely on pollen and nectar, but the larvae of the species are fierce predators that sometimes display cannibalistic behavior.

Human Cerebrum Thin Section - The cerebrum is divided into two hemispheres by a deep groove termed the longitudinal cerebral fissure. Each side of the cerebrum is active in different functions. The right side of the cerebrum controls activities such as orientation, awareness, depth perception, and facial recognition. Creativity is also often associated with the right hemisphere. The left hemisphere is associated with logic, numbering skills, reasoning, and language.

Human Erythrocytes - The compositional difference between blood types lies in the specific kinds of antigens found on the surface of the red blood cells. Antigens are protein molecules that provide the biological mark of an individual's blood and tissue type. When different types of blood are mixed within the body, the reaction can be fatal as red blood cells burst and the kidneys fail. Today, there are 27 known human blood groups. Understanding blood compatibility issues has had a revolutionary effect on the field of medicine.

Insect Wings - Insects use their wings to accomplish feats that pilots can only dream of. Their aerodynamic acrobatics have fascinated scientists for years, and the old conviction that bumblebees should not be able to fly has finally been undeniably dispelled. Recent studies in the area of fluid aerodynamics have shed a significant amount of light on insect wings and flight.

Kidney Tissue Thick Section - Mouse kidneys are located on the upper wall of the abdominal cavity and are held in place by fibrous capsules. Similar to other mammalian kidneys, mouse kidneys appear bean shaped, brownish red, granular, and have a firm consistency. The outer region of the kidney is termed the cortex and the inner area is known as the medulla. Tiny structures called nephrons, which consist of even smaller and more intricate elements, stretch across both sections. The nephrons are the functional units of the kidneys, responsible for filtering blood, reabsorbing water and nutrients, and secreting wastes.

Luna Moth Wing Scales - Due to their striking beauty, luna moths are often reared in captivity. They are an integral part of the lucrative lepidopteran trade, and dried adults, live eggs, larvae, and pupae are often sold for profit. Unfortunately for collectors, however, this species is not as vibrant in death as it is in life. Dried specimens fade to a pale yellow, leaving only a faint shadow of what was once a dazzling, luminous green.

Meiosis in Grasshopper Testes - Members of the order Orthoptera, grasshoppers are well known for their amazing jumping ability. Despite their small size, grasshoppers can cause a tremendous amount of damage if present in large numbers. They are capable of destroying entire crops of alfalfa, clover, cotton, corn and other grains, resulting in millions of dollars in crop damage every year.

Mosquito Proboscis - There are over 2500 different species of mosquitoes throughout the world and most do not stray more than a mile away from their breeding site. Female mosquitoes need water to lay their eggs. They can produce 100-300 eggs at a time, forming groups that float upon the water's surface like rafts. Areas nearby creeks, lakes, and other slow moving or standing water are, therefore, the most heavily inhabited and should be avoided if one wants to avoid the dreaded mosquito bite.

Mouse Intestine Thick Section - Not all mice attain the fame of such greats as Mickey, Jerry, and Mighty Mouse. However, many are significant in other ways, especially as laboratory animals. Their large intestines are very similar to those of other vertebrates, the primary function of which is to absorb water and electrolytes from digestive residues and to store fecal material.

Paramecium Conjugation - The Paramecium genus contains numerous species of single-celled microscopic organisms that appear much like a lady's slipper surrounded by tiny hair-like appendages termed cilia. The miniature protozoan glides through water by a coordinated movement of its cilia like millions of miniature oars. Paramecia are generally found in slow moving and still bodies of freshwater, especially in areas containing large amounts of pond scum, which is rich in algae.

Potato Starch - The value of a potato has had its ups and downs over the past few thousand years. During some moments in history, potatoes were shunned because they were believed to be poisonous. Yet, in other periods, such as the Alaskan Klondike gold rush, they were quite literally worth their weight in gold.

Ramie Fibers - The long, glossy ramie fibers are naturally white and have an almost silky appearance. Ramie is a cellulosic substance as is cotton, linen and other plant fibers. The inner structure of ramie, however, differs from the other plant fibers that contain polymeric carbohydrate structural components. The physical form of the cellulose in the Ramie fiber is very rigid and crystalline but is extremely porous, which provides it with better absorbency than many other cellulose fibers. One of the strongest natural fibers, ramie exhibits even greater strength when wet.

Saccharomyces Yeast Cells - Members of the Saccharomyces genus of yeast fungi have a direct impact on the daily lives of society. Whenever a dinner roll is nibbled or a glass of wine sipped these microorganisms are largely responsible. One of Saccharomyces' many species is employed primarily for the fermentation of sugars in the winemaking process, while another is useful for the rising of bread.

Spirogyra Filamentous Algae - During times of environmental strain, such as extended droughts or heat waves, members of Spirogyra switch from asexual to sexual reproduction. Genetic material is exchanged via temporary conjugation tubes established between neighboring strands, or even cells from the same strand, forming an egg-shaped, orange zygospore. The cell wall of the zygospore is thick and adapted to surviving harsh conditions. The zygospore emerges as a new algal strand once the environment is more favorable.

Surirella gemma Diatom Frustule - Diatoms are one of the most abundant plants on the Earth. Usually classified in the family Bacillariophyceae, these unicellular algae live in both fresh and salt water. Their extensive fossil record has made them a favorite tool of ecological researchers.

Termite Claw - Surprisingly, these members of the insect order Isoptera may be likened to cows. Both species have a hugely modified, multi-compartmented stomach developed for digesting a cellulose-based diet. Termites are generally dreaded by homeowners but play an important part in wildlife ecology. They provide food for more amphibians, reptiles, and birds in the tropics than any other insect.

Water Fleas (Daphnia) - Daphnia are small in size, but large in purpose. These microscopic crustaceans, belonging to the order Cladocera, are more populous than ants, found worldwide, and essential for the fishing industry. They are nicknamed water fleas due to their characteristic hopping motion and resemblance to the common flea.

Whipworms (Trichuris) - Parasitic members of the Trichuris genus, commonly referred to as whipworms due to the whip-like body form of the adults, contain numerous species that affect a wide variety of mammals, including humans, cattle, rodents, cats and dogs.

Zygnema Green Algae - A common sight floating atop stagnant water, algae of the genus Zygnema can be identified microscopically by its two star-shaped chloroplasts per cell. Found often alongside Spirogyra, another still water green algal genus, Zygnema filaments combine to form green or yellow-brown mats and can reproduce sexually or asexually, including vegetatively.