Answer:
primary; counter; Gram-positive; Gram-negative
Step-by-step explanation:
The illustration is about the Gram-staining procedure.
The procedure is used to distinguish between the bacteria that have a thick cell wall capable of retaining the color of a dye (Gram-positive) or otherwise (Gram-negative).
A smear of the bacterium to be tested is heat-fixed to a clean glass slide after which a suitable primary stain is added, allowed to stay for a few seconds, and rinsed. A mordant is then added, rinsed before a counter-stain is added, and also rinsed. The slide is then allowed to drain off water and then viewed under the microscope using the oil immersion. Gram-positive bacteria will appear blue or purple, taking up the color of the stain while Gram-negative bacteria will appear red under the microscope.