You can improve image contrast by regulating the opening of the diaphragm. This  deflects the light rays from the edge of the diaphragm and causes them to enter the specimen  at an angle. Such scattering makes the specimen look darker. Cells and sub cellular structures may contain natural pigments (e.g., chlorophyll in  chloroplasts and hemoglobin in red blood cells) that provide contrast and make these structures  visible. However, many cells and parts of cells are translucent. One way you can improve  contrast is to use dyes or stains that bind to or are taken up by various sub cellular structures,  which then absorb enough light to provide contrast. In your laboratory work with the microscope, many of your observations will be of living  organisms or tissues or parts of organisms that you will want to keep alive. To allow them to  dry out greatly distorts them, to say nothing of the effect death has on a study of their  movements. To observe living material, prepare a wet mount of a drop of water containing protozoa  or algae provided your instructor. (Since your specimen is already immersed in water, there is  no need to add tap water in making your wet mount. However, if your preparation begins to  dry out while under observation, add 1 drop of water at the edge of the cover slip.) Excess water under the cover slip can be soaked up by carefully touching a piece of  tissue (Kimwipe) to the edge of the cover slip. Prepare additional wet mounts from the other samples provided by your instructor. Do  not be too hasty in discarding a slide because you don’t find any microorganisms; a systematic  survey of the preparation is often necessary to locate them. Try to identify the microorganisms  you observe, using books on the instructors bench or by the materials in the notes section of  the General Biology web pages. To identify the smaller organisms, you may have to use the  high-power objective. If the organisms are moving too fast mix a drop of protoslow with your  sample. Draw what protozoans you observed in the laboratory questions section at the end of  this lab. Be sure to include the magnification you observed your specimens in. Prepare a wet mount of anion epidermal tissue, following the procedure demonstrated  below. Examine this tissue under low power objective. The "lines" that form the network between the cells are non,living cell walls composed  chiefly of cellulose. The cell wall surrounds the  plasma membrane , which encloses the  cytoplasm . The central part of many plant cells (which is difficult to observe in living cells) is  taken up by a  vacuole  that is filled with water and salts. Next examine the cells under high power. Locate the  nucleus , which appears as a  dense structure in the translucent cytoplasm. Note that in some cells, the nucleus looks circular  and seems to be lying in the central part of the cell. In other cells it seemes to be compressed  and pushed against the cell wall. The central vacuole, nucleus, and cell wall are separated from the cytoplasm by  membranes, but the membranes are difficult to observe in the preparation that was used.  STUDY OF PLANT CELLS: STUDY OF PROTOZOA AND ALGAE: