1. Reticular theory: According to the scientist Frommann (1865), protoplasm is formed by reticular fibers on the base material.
2. Granular theory: According to the scientist Altman (1886), protoplasm is a granular fluid with numerous small and large biomass.
3. Alveolar theory: According to the scientist Butschli (1892), protoplasm is like soap foam with numerous alveoli or tiny bubbles.
4. Colloidal theory: According to scientists Wilson and Fisher (1894), protoplasm is partly liquid and partly colloidal.