[...]... 17 Complete the following for the 10 × objective: a _ ocular micrometer divisions = _ stage micrometer divisions b _ ocular micrometer divisions = 1 stage micrometer division = _ mm c One ocular micrometer division = _ stage micrometer divisions = _ mm 18 Complete the following on units of measurement: Unit Abbreviation Value a 1 centimeter 10–2 meter b 1 millimeter mm c ... tube by turning the coarse adjustment knob counterclockwise until the object comes into view Once the object is in view, use the fine adjustment knob to focus the desired image 6 Open and close the diaphragm, and lower and raise the condenser, noting what effect these actions have on the appearance of the object being viewed Usually the microscope is used with the substage condenser in its topmost position... is not being used with oil Oil causes the coverslip to float since the coverslip sticks to the oil and not the slide, making viewing very hazy or impossible Insufficient light passing through the ocular Lint, dust, eyelashes interferring with view Particles seem to move in hazy visual field 8 After you are finished with the microscope, place the low-power objective in line with the ocular, lower the... place Removing a slide when the higher objectives are in position may scratch the lenses (6) A note about wearing eyeglasses A microscope can be focused; therefore, it is capable of correcting for near- or farsightedness Individuals who wear eyeglasses that correct for near- or farsightedness do not have to wear their glasses The microscope cannot correct for astigmatism; thus, these individuals must... biological safety cabinets should be used whenever procedures are conducted that have a high potential for generating droplets These include activities such as blending, sonicating, and vigorous mixing xiv © The McGraw−Hill Companies, 2002 4 Mechanical pipetting devices should be used for manipulating all liquids in the laboratory Mouth pipetting must not be done, 5 Use of needles and syringes should be... flagella having a long wavelength and about one helical turn P aeruginosa is widely distributed in nature and may be a saprophytic or opportunistic animal pathogen B cereus is found in a wide range of habitats and is a significant cause of food poisoning S volutans occurs in stagnant freshwater environments Principles Many bacteria show no motion and are termed nonmotile However, in an aqueous environment,... microscopy is useful in observing unstained living microorganisms, microorganisms that are difficult to stain, and spirochetes (figure 3.2), which are poorly defined by bright-field microscopy 17 Harley−Prescott: Laboratory Exercises in Microbiology, Fifth Edition I Microscopic Techniques 3 Dark−Field Light Microscope Figure 3.1 Dark-field Microscopy Dark-field microscopy can best visualize transparent,... Principles Certain transparent, colorless living microorganisms and their internal organelles are often impossible to see by ordinary bright-field or dark-field microscopy because they do not absorb, reflect, refract, or diffract sufficient light to contrast with the surrounding environment or the rest of the microorganism Microorganisms and their organelles are only visible when they absorb, reflect, refract,... or the rest of the microorganism Microorganisms and their organelles are only visible when they absorb, reflect, refract, or diffract more light than their environment The phase-contrast microscope permits the observation of otherwise invisible living, unstained microorganisms (figure 4.1a–d) In the phase-contrast microscope, the condenser has an annular diaphragm, which produces a hollow cone of light;... Laboratory Exercises in Microbiology, Fifth Edition I Microscopic Techniques 1 Bright−Field Light Microscope and Microscopic Measurement of Organisms © The McGraw−Hill Companies, 2002 Review Questions 1 Differentiate between the resolving power and magnifying power of a lens What is meant by the term “parfocal”? 2 Why is the low-power objective placed in position when the microscope is stored or carried? 3 Why . droplets. These include activities such as blending, sonicating, and vigorous mixing. xiv Summary of Universal Precautions and Laboratory Safety Procedures 4. Mechanical pipetting devices should be used. concepts of general microbiology as a whole and of the individual applied fields. The protocols vary in content and complexity, providing the instruc- tor with flexibility to mold the laboratory. available time and equipment, and confines and scope of the course. Fur- thermore, it provides a wide spectrum of individual exercises suitable for students in elementary and ad- vanced general microbiology