Bresser National Geographic 90-39001 Mode D'emploi page 14

8.2. Textile fibres
Objects and accessories:
1. Threads of different textiles: Cotton, linen, wool, silk, Celanese, nylon and
any others you can find.
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 magnification. Cotton fibres are
of plant origin and look, under the microscope, like a flat, twisted band. The fibres
are thicker and rounder at the edges than in the centre. Cotton fibres consist pri-
marily of long, collapsed tubes. Linen fibres are also of plant origin; they are round
and run in straight lines. The fibres shine like silk and exhibit numerous swellings
along the shaft of the fibre. Silk is of animal origin and consists of solid fibres of
smaller diameter than the hollow vegetable fibres. Each silk fibre is smooth and
even and has the appearance of a small glass rod. Wool fibres are also of animal
origin; the surface consists of overlapping scales, which appear broken and wavy.
If possible, compare wool fibres from different weaving mills, and note the differ-
ences in the appearance of the fibres. Experts can determine the country of origin
of wool based on its appearance under a microscope. Celanese is artificially manu-
factured by a long chemical process. All Celanese fibres show hard, dark lines on a
smooth, shining surface. The fibres crinkle in the same way after drying. Observe
the similarities and differences between the different fibres.
8.3. Saltwater brine shrimps Accessories:
1. Brine shrimp eggs (23d)
2. Sea salt (23c)
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
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3. Hatchery (21)
4. Yeast (23a)
sometimes die off. During drought conditions, to ensure that the species will repopu-
late 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, fill 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!
8.3.4. Feeding your Artemia salina
Feed your brine shrimps often to keep them alive. The best food is dry powdered
yeast (23a). Give them some every other day. Be careful not to overfeed them, as
doing so can cause the water to stagnate and poison the brine shrimps. If the water
does begin to stagnate (you'll see it darkening), transfer the brine shrimps to the
fresh saline solution you have prepared earlier (see 8.3.2).