In cellular biology, inclusions are diverse intracellular[1] non-living substances (ergastic substances)[2] that are not bound by membranes. Inclusions are stored nutrients/deutoplasmic substances, secretory products, and pigment granules. Examples of inclusions are glycogen granules in the liver and muscle cells, lipid droplets in fat cells, pigment granules in certain cells of skin and hair, and crystals of various types.[3] Cytoplasmic inclusions are an example of a biomolecular condensate arising by liquid-solid, liquid-gel or liquid-liquid phase separation.
These structures were first observed by O. F. Müller in 1786.[1]