Выражение встречается в следующем контексте:
Transfer to the filtration funnel the total volume
of a solution pool or of a single unit, and apply vacuum. If needed, add stepwise
a portion of the solution until the entire volume is filtered. After the last addition of
solution, begin rinsing the inner walls of the filter holder by using a jet of particle-
free water R. Maintain the vacuum until the surface of the membrane filter is free
from liquid. Place the filter in a Petri dish and allow the filter to air-dry with the
cover slightly ajar. After the filter has been dried, place the Petri dish on the stage
of the microscope, scan the entire membrane filter under the reflected light from
the illuminating device, and count the number of particles that are equal to or
greater than 10 µm and the number of particles that are equal to or greater than
25 µm. Alternatively, partial filter count and determination of the total filter count
by calculation is allowed. Calculate the mean number of particles for the
preparation to be examined.
Заранее спасибо