Question

Why should one place a drop of glycerin over the specimen?

Answer 1

Resolving power of a microscope is it's ability to distinguish the objects placed very close. In case of microorganism those objects are organells of that microorganism. We can increase the resolving power of microscope by increasing the refractive index of medium between object and microscopic objective lens or we can say aperture,

Therefore to increase the refractive index we add a drop of glycerine or water on microorganism before covering it with cover slip.