In 1898, Friedrich Loeffler and Paul Frosch found evidence that the cause of foot-and-mouth disease in livestock was an infectious particle smaller than any bacteria. This was the first clue to the nature of viruses. A virus is a structure of protein coat(capsid) surrounding a nucleic acid core. The question that creates divides is whether a virus is alive or not . Viruses depend on the host cells that they infect to reproduce and in order to be considered alive the main characteristics is that all life reproduces itself and since viruses are unable to that by themselves they are nonliving. Proving that viruses are not alive Wendell Stanley came to the conclusion that they are not alive since it could be crystallized and all life dies without water. While Stanley considered viruses not living Dimitre Ivanowski thinks otherwise. Since Ivanowski found that the disease is contagious and this has to be caused by something living. Even though both scientists discovered differences in the virus there are still characteristics that compare living and nonliving. Viruses contain DNA/RNA which codes the virus elements and that mutates just like ours and we are life, a virus does not belong to a characteristic of living or nonliving it belongs in a branch of its own. While viruses take over a host cell to become "living" they are just considered parasitic. An organism that has a metabolism that functions on it own is living and since a virus requires a host cell to do such thing. Viruses cannot reproduce without a host, react to their environment, and growing to increase their biomass without the host cell. They inject their mRNA and attach themselves to living organisms, and since they can only be considered living with a host cell they are nonliving separately.