Paramecium

This Paramecium has been lightly stained with neutral red dye, a type of biological stain that can be used with living cells. Neutral red turns bright red in the presence of acid. The many small red dots seen in this subject are lysosomes, the bodies that produce the acids and carry the enzymes needed for digestion. The larger red spheres are food vacuoles--filled with bacteria, digesting in the bath of acids and digestive enzymes delivered by the lysosomes.