Which one is Phase Contrast?
Which one is Differential Interference Contrast?
Phase Contrast and DIC Comparison Image Gallery
Phase contrast and differential interference contrast (DIC) should be considered as complementary (rather than competing) techniques, and employed together to fully investigate specimen optical properties, dynamics, and morphology. In many cases, each technique will reveal specific details about a particular specimen that is not apparent from observing images captured by other methods. The wide variety of images presented in this gallery are derived from both thick and thin transparent specimens, as well as specimens that have inherent contrast originating from synthetic dyes (stains) or natural pigments.
All true teeth have certain characteristics in common and are composed of three layers. The innermost section of a tooth is the pulp, which consists of small blood vessels, cells, and a nerve. The pulp nourishes the dentine that is similar in composition to bone and comprises the bulk of each tooth. Enamel (illustrated above), the hardest substance of the body, covers the dentine of the tooth's crown. Due to the enamel, the teeth of mammals are the part most often fossilized and since the number, size, organization and shape of the teeth are different in every species, they are extremely useful for taxonomy.
Mammalian teeth have evolved into different forms because they are used for different purposes. Elephant tusks, which can be used for defense and for lifting, are actually modified incisors and are the largest teeth in the world. The lower incisors of pigs are close together and projected forward so that they can be used as a tool for digging. Baboons feature enlarged canine teeth that are utilized for defense and display. However, the sawfish may be the most unusually adapted since it is the only animal with true teeth outside its mouth. Members of the species utilize the teeth on the sides of their snouts to lacerate prey.
Nucleic Acid Stains in Animal Cells
Cells are the basic building blocks of all living organisms. While describing plant tissues in 1665, Robert Hooke first coined the term because the cellulose walls of cork that he was able to see through his microscope reminded him of the cells inhabited by monks. The images presented below compare a thin section of animal tissue stained for the nucleic acids RNA and DNA.
The finer points of cellular purpose and composition were not understood form many years, slowly developing as microscopes improved. In fact, the realization that cells were the fundamental unit of plants and animals did not occur until the 1830s. Previously cells had been believed to be simply pores, but the detection of nuclei and moving protoplasm put an end to the misconception. For other discoveries, additional microscopical enhancements needed to be made. Walter Flemming's advanced methods of fixing and staining cells, for instance, facilitated his observation of chromosome transmission between cells and led to his very precise account of mitosis and cell division in 1882.
Recent experimentation has been aimed at utilizing animal cells for human recovery from diseases, such as Parkinson's. Scientists hope to use cloned cells to replace improperly functioning cells in patients, thereby reducing tremors and other symptoms. Although the research is in its early stages, if it proves successful the medical world could be revolutionized. However, concerns such as the possibility of transmitting animal disease to humans through cell transplantation and the ethics of genetic cloning are problems that may hinder future developments.
Lichen Thallus
The classification of lichens has been tremendously problematic for taxonomists. Once thought to be a single organism, microscopy revealed that lichens are a structure composed from a symbiotic relationship between two distinct organisms, fungi and algae. Although each individual species can flourish independently, in certain harsh environments they must work together in a mutually beneficial relationship in order to endure.
Certain characteristics make algae and fungi extremely useful to each other. Algae form simple carbohydrates that are excreted and subsequently absorbed and transformed by fungi cells. Algae also produce several vitamins that are required by fungi. In return, fungi absorb water vapor from the air and provide shade for the algae, which are very sensitive to light. Working together in such ways enables lichens to colonize extremely inhospitable areas, including bare rock, solidified lava flows, and regions at temperature extremes.
Fungi and algae retain their individual genetic make-up even in symbiosis, but the composite body they form is known as a thallus. The shape and appearance of lichens is dependent on the species of fungi present, not the algae. Lichens grow relatively slowly and their propagation is unclear. Scientists generally agree, however, that the most frequent kind of lichen reproduction is vegetative, a portion of an existing lichen breaking away and starting a new growth in an adjacent area.
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