What is better, making a prep using a lot of material or various different preps using a lower quantity of material in the sample?
A sample using a lot of material (plankton and debris) hinders observation. Many organisms are found under other ones or among masses of debris which sometimes inhibits identification. The best approach is to extract a small drop of the sample, pour it over a cover glass and, according to the density of the material observed with the naked eye, add an adequate quantity of sea water with the Pasteur pipette to dilute and clean the organisms present in the initial droplet. With a little practice one learns to measure the adequate amount of liquid for the size of the cover glass.
Can you use any dye for microscopes that makes sample observation easier?
Yes, you can. The so-called ‘vital’ dyes, frequently used for live dyeing, can be used. These are easy to purchase and prepare, such as methylene blue, neutral red, Bengal pink, etc. They facilitate the identification of organisms which were alive at the moment of sampling, as well as allowing some cellular organelle observation. Likewise, some other more complex dyes can be used (carmines, haematoxylins, etc.) These require more sophisticated dye and tinction preparation methods. In any case, the most delicate moment is usually the process of washing the sample, since many plankton organisms in the sample can be lost when carrying out these processes. If you have a laboratory centrifuge (even a manual one), tinctions and washings can be easily carried out using a global volume of the plankton sample instead of tinctions between Petri dishes and cover glasses.
Once the material of a prep has been observed by microscope, can you put it back in the jar containing the original sample?
It is not advisable. The material that has been used in microscope observation for a few hours has been exposed to heat from the microscope’s lighting system, to the weight and movement of cover glasses and to evaporation. Therefore, many organisms will be deteriorated, with broken or torn parts, etc. Hence, returning them to the original sample would only diminish its quality for future observations, so getting rid of this material is recommended.
How can I change the position in which an organism appears in the wet prep in order to observe better the details that help to identify it?
If you observe a specific organism in an inadequate position to visualize the necessary details for its identification, you can change its position by changing to lower magnification (so as not to lose sight of the observation field) and carefully moving the cover glass with the handle of a dissecting needle, or by adding a small droplet of sea water in the closest edge of the cover glass. In both cases, fluid streams will be created which will ‘drag’ the organism, allowing it to be seen from alternative positions. It is important to bear in mind that the cover glass should only be moved if a sufficient amount of liquid remains below it and it is not too dry. If this were not the case, the cover glass would move with more difficulty and it would also break a greater number of structures.
How can I select a specific organism observed in the binocular loupe (stereomicroscope) to separate it and observe it at higher magnifications in the microscope?
Once this organism has been identified under the binocular loupe, select an adequate magnification to get a good view of the organism, of the surrounding field and an acceptable depth of field, and use a Pasteur pipette whose opening has been previously made finer with an alcohol burner, by stretching and cutting its tip. Carefully bring that opening closer to the organism and suck it out. Place it in a Petri dish in which previously a small droplet of sea water has been placed. Before placing the cover glass, make sure the organism has been deposited by observing it under the binocular loupe or with the microscope at low magnification. Place the cover glass carefully, ensuring that the organism is not left out of it.
How long can I keep a wet prep for deferred microscope observation?
A wet prep can be preserved for a long time (hours) in observation with the microscope if drying up by evaporation is avoided, adding sea water at the edge of the cover glass every ten to fifteen minutes, depending on the temperature. If you wish to preserve that prep for a deferred observation, i.e. on the next day, it is advisable to create a ‘wet chamber’ to keep it at a minimum level of evaporation. This ‘wet chamber’ can be easily made with a Petri dish where a base of cellulose paper, cotton wool or foam, soaked in distilled water. Place the prep you want to preserve over any stand on this surface, covering it with its corresponding lid. As long as the wetness of the chamber is preserved, the prep will be preserved adequately, even for two or three days.
Is it possible to take any photograph with a microscope in a fast and easy way?
It is easy to take acceptable quality microphotographs with standard microscope, mono or binocular. You can use a compact digital camera, a mobile phone or a tablet, taking advantage of the afocal optics of these devices. Once the organism to be photographed has been selected and perfectly focused in the microscope, simply place the device’s camera you are using close to the eyepiece till the target organism is visible in the screen. You should keep the optical axis of the microscope system and the camera perpendicular, and simply adjusting the lens. When it appears clear and focused you can take the photo. It does not really matter if the organism is seen surrounded by a circle, since it is possible to cut and select the part of the image to be used ultimately with any simple image editing programme, as well as improving the image with changes in brightness, contrast, colour balance, etc. With just a few attempts you will get the necessary practice to take acceptable microphotographs if you do not have specific microphotographic devices.