Viruses are smaller than bacteria and transmissible from diseased to healthy organisms. They can only multiply in their living host and outside they are non-living. Viruses are given as vaccines in small doses and are effective against the disease, but are resistant to germicides. There are many shapes viruses can exist in, spherical, golf-ball shaped, rod-shaped, tadpole like, helical, and polyhedral shaped. Viruses in plant are extremely small, smaller than bacteria. The chemical structure in viruses is simple. The core is made up of nucleic acid either DNA or RNA, it can not have both. It's infectious properties are dependent on the kind of nucleic acid is in the core. The core is surrounded by a protein coat called a capsid. Viruses lack a cytoplasmic membrane, and can only replicate inside the host cells. Outside the host it is non-living so it shows no growth, development, nutrition, and reproduction. As living organisms they have genetic material, definite races and strains, and exhibit mutations. Viruses are the only organisms that show the bridge between living and not living.