Evening star. [volume] (Washington, D.C.) 1854-1972, 1929-06-09

from different depths In various lakes. Ordi-
nariy, the centrifuge is run at a speed OF
$4,000 revolutions minute, the water sample
being fed slowly into the separator, with the
result that the organisms churned from the
water, and are deposited on the sides of the
special steel bowl, from which position they are
removed subsequently for scientific indentifica-
ton and study.
The quantity of organic matter in the plank
ton of Wisconsin lakes ranges from 700 to
5000 milligramS per cubic meter of water. The
remarkable centrifuge is the only type of ap-
paratus capable of separating the minute or
ganisms from the water where they live. It
permits Of recovering and identifying from one-
third to onehalf of all the invisible bacteria in
lake-water sample, as well as 81 per cent OF
the larger forms of life.
Special water bottleS-adjuStable metal con-
tainerS-whch collect from one to three lterS
of lake water at time-are used. Their con-
struction is such that they can be lowered to
the desired depths in the lake. A trip trigger
is then pulled which opens the bottles and
closes them again as soon as they are filled
with water The organic content of the lake
can be estimated from these specimens, while
material IS also obtained for fish-food studies.
The number of water samples taken varies
with the size and depth of the lake. Such food
as water fieas as large as pinheads-the favorite
food Of game fish-are studied In each lake as
well as the particular plants upon which these
deaS feed
SAMPLES of water are analysed chemically
to ascertain the amounts of phosphates and
nitrates present, as well as the content Of
oxygen, carbon dioxide chlorine and other ma
terialS which influence fish life. Temperatures
Of the water at various depths are taken with
special thermometers. while scientific surveys
of the algae growing in the different lakes ara
also made. The extent of tiny animal life in
these lakes is determined
There Is an intimate correlation existent
between the plant and small animal life and
the fish content of each lake Small fish, for
example, cannot prosper Unless plenty OF
crustacea occur, while the population of large
game fish depends proportionaly on the album
dance of small fish which the former consume
AS result of fish research of this kind one
expert estimated the fish population of a Ger.
tain Wisconsin lake Is miles in circumference
at 100000 Lake trout. whitefish and ciscos
prefer to live in the cool lower waters Of an
inland lake. while bass and sunfiSh thrive In
the warmer surface waters.
Many of the Wisconsin lakes studied are
practically virgin territory, far removed from
the beaten paths Of civilization and hence free
from the pollution which usually develops
when the shores of such bodies of fresh water
are populated to capacity. It is thus possible
to make conclusive comparisons of uninhabited
and habited lakes to ascertain the longtime
effects Of mans presence on fish increase an.
nual growth and well-being.
The rate Of sunlight penetration has been
studied by means of special apparatus developed
expressly for that purpose. Large aquatic
plants which are essential in the successful
life cycle Of game fish depend upon sunlight for
growth. Some lakes are stained with peat and
other dark-colored SOILS while others are dis.
colored by falling leaves and wind blown vege.
tation. DR.. Birge reports that per cent Of the
suns energy viii penetrate to o depth OF IS
feet I'm clear, sparkling. fresh-water lake. In
dark and discolored lake water, similar