Composition and Biomass of Phytoplankton
145
is slid gently to the side and removed without disturbing the lower two slides.
Simultaneously, a coverslip can be slid over the hole of the middle slide as the upper
chamber is removed. Alternatively, the material in the hole of the middle slide can
be evaporated to dryness and then the second slide can be separated from the third
by gently inserting a r azor blade between them at one corner. The algae then can be
either counted directly or mounted permanently in ordinary fashion.
MICROSCOPE CALIBRATION PROCEDURES
It is necessary to calibrate each microscope against a known scale, since every
instrument differs in magnification according to the combination of oculars and
objectives. A marked glass disc, termed a Whipple ocular micrometer (or reticule,
iIIIl
Figure 10.4. The rulings of a Whipple ocular micrometer reticule.
Micrometer Scale
I I I I I I I I I I I I
~~-------------l nun--------------4,1.,-------------- l~aun~-------------.~1
EnlargemO!tlt of Micrometer Scale
Figure 10.5. A stage micrometer with the scale enlarged. [From Jackson and Williams (1962).]