Cellulase is homopolysaccharide. The cellulose is digested by the micro-organism (bacteria and protozoans) in the alimentary canal of herbivorous mammals. These micro-organisms live as symbionts in the stomach of ruminanats (buffallow, cow) and in the intestine of horse and donkey. The bacteria and protozoans ferment cellulose into short chain fatty acids such as acetic acid and propionic acid and then are absorbed and utilized by the animals. The viruses lack their own merabolic. maschinary and enzyme system, therefore, they cannot digest the food materials.