Bresser NATIONAL GEOGRAPHIC 40X-1280X Instrucciones De Uso página 14

picture from the newspaper consists of many small points, which appear somewhat
dirty. The pixels (raster points) of the magazine image appear sharper.
8.2. Textile fi bres
Objects and accessories:
1. Threads of different textiles: Cotton, linen, wool, silk, Celanese, nylon and
any others you can fi nd.
2. Two needles:
Put each thread on a glass slide and fray each with the help of the two needles. Put
a drop of water over each thread with the pipette and cover each with a cover glass.
Adjust the microscope to a low magnifi cation. Cotton fi bres are of plant origin and
look, under the microscope, like a fl at, twisted band. The fi bres are thicker and
rounder at the edges than in the centre. Cotton fi bres consist primarily of long, col-
lapsed tubes. Linen fi bres are also of plant origin; they are round and run in straight
lines. The fi bres shine like silk and exhibit numerous swellings along the shaft of
the fi bre. Silk is of animal origin and consists of solid fi bres of smaller diameter than
the hollow vegetable fi bres. Each silk fi bre is smooth and even and has the appear-
ance of a small glass rod. Wool fi bres are also of animal origin; the surface consists
of overlapping scales, which appear broken and wavy. If possible, compare wool
fi bres from different weaving mills, and note the differences in the appearance of
the fi bres. Experts can determine the country of origin of wool based on its appear-
ance under a microscope. Celanese is artifi cially manufactured by a long chemical
process. All Celanese fi bres show hard, dark lines on a smooth, shining surface.
The fi bres crinkle in the same way after drying. Observe the similarities and differ-
ences between the different fi bres.
8.3. Saltwater brine shrimps
Accessories:
1. Brine shrimp eggs (23d)
2. Sea salt (23c)
3. Hatchery (21)
4. Yeast (23a)
14
CAREFUL!
These eggs are not fit for human consumption.
8.3.1. Winter eggs of Artemia salina
Artemia salina are species of brine shrimp typically found in salt lakes — bodies of
water with a higher salinity than even the ocean. During a drought, a salt lake can
become a hostile habitat for organisms, and entire populations of Artemia salina
sometimes die off. During drought conditions, to ensure that the species will re-
populate the salt lake when the drought ends, Artemia salina lay thick-shelled eggs
called winter eggs that can survive for up to ten years in a dormant state. Winter
eggs can withstand heat, cold and chemicals. These eggs hatch when favourable
conditions return to their ambient environment. The eggs provided (23d) are of
this type.
8.3.2. Hatching winter eggs
To hatch the brine shrimps, create a solution with an appropriate salinity and tem-
perature. First, fi ll two containers with a half litre of freshwater each, and let them
both stand for about thirty hours. Next, pour half of the provided salt (23c) into one
container and stir the solution until the salt dissolves. Pour some of this solution
into the hatchery (21). Place a few eggs close to the lid. Position the hatchery
somewhere with plenty of light but not in direct sunlight. The ambient temperature
should ideally hover around 25 °C. As water in the hatchery evaporates, gradually
add freshwater from the second container. After two to three days, the eggs will
hatch brine shrimp larvae, called nauplii.
8.3.3. Observing Artemia salina under a microscope
Using the pipette (20a), move some larvae from the container to a microscope slide
for examination. When viewing the larvae, you'll notice that they swim through the
solution using hairlike limbs! Each day, examine a few more. You can even view the
entire hatchery under the microscope if you remove its lid. The larvae will mature in
six to ten weeks, depending on the temperature of the water. Soon, you will have
an entire generation of saltwater brine shrimps that reproduce frequently!