To most people it may seem mystifying that the "wonder drug" have had so much success against the bacterial diseases and so little success the virus diseases. Since viruses, after all, can cause diseases only if they reproduce themselves, why should it not be possible to jam the virus's machinery just as we jam the bacterium's machinery? The answer is quite simple, and indeed obvious. Once you realize hoe a virus reproduce itself., As a complete parasite, incapable of multiplying anywhere except inside a living cell, the virus has very little, if any, metabolic machinery of its own. To make copies of itself, it depends entirely on materials supply by the cell it invades. This ,however, it can do with great efficiency. One virus within a cell can become 200 in twenty-five-minutes. And it is therefore difficult to deprive it of those materials or jam the machinery without destroying the cell itself. Biologist discovered the viruses only recently, after a series of encounters with increasingly simple from of life.