They noticed that porcelain candles that were normally used to filter samples were unable to sterilize or stop the infectious nature of their respective diseases. Along with some studies on the nature of warts a separation was made. All cells, including bacteria, replicate or reproduce themselves, whereas viruses are replicated or reproduced.
Hence the known fact that viruses lack the machinery of living cells to generate biochemical energy and utilize it, and therefore they are dependant on living cells for their reproduction. With this new development in their understanding, researchers had to now accept the notion that viruses represent chemical matter rather than some mysterious biological phenomena. With this notion, viruses could now be isolated, purified and characterized much like the known table of chemicals.3,4 .
The classification of viruses finds its roots in Linnaeus's classical system of families, genera and species. In their terminology, an agreed-upon family name ends in viridae, subfamily names end in virinae and genera, like species, ends in virus.4 From this classification method, the question about the nature of viruses, living or nonliving, arises. In order to answer this, a definition or criteria for life itself must be established. .
The criterion seems to be fundamentally sound from definition to definition. The first lies in the act of different proteins, mostly enzymes, to cooperatively produce and use chemical energy for the synthesis of macromolecules such as nucleic acids. The second criterion allows the nucleic acids to carry in their structure the mechanisms for the coding and deciphering of information that is needed for the production of those macromolecules.7 .
With regard to these fundamental criteria, viruses seem to be lacking the essentials for life. The early discovery that viruses could not be cultivated outside the living cell indicated that alone, they are not fully alive.