Word: virus
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Dates: during 1960-1969
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...dozen different viruses have been found to cause cancer in mice, and they show a bewildering variety of behavior. Some are clearly inherited. One is passed on from generation to generation in mouse-mothers' milk, so daughter mice develop breast cancer. A male mouse may be a healthy carrier of this virus and infect a female with which he is mated...
Mice that show no signs of harboring a leukemia virus may develop the fullblown disease, and produce the virus plentifully, after they are exposed to X rays...
Still more confusing are the crossovers between species. Millions of monkeys carry a virus which apparently does them no harm. But this virus, known as SV-40, may cause tumors if injected into hamsters. Viruses found in human tissues and in some rat cancers make hamsters bear deformed young with features resembling human mongolism. One virus that normally causes only grippe in man will cause cancer in hamsters...
...Packaged Virus. Most baffling of all are the disappearing tactics of viruses involved in cancer. In one rabbit tumor, the virus cannot be detected in new, dividing cells, but is readily found in old cells where it has already done its damage. This seems to be a case, says the Sloan-Kettering report, of "the more active, the less evident." And it is the opposite of the situation in most viral infectious diseases, in which the virus abounds and is easily detectable as the fever approaches its climax, because infected cells are then mass-producing new virus particles...
...structure of many viruses in their conventional forms is well known. They consist of a core of nucleic acid-either ribonucleic acid (RNA) or deoxyribonucleic acid (DNA)-wrapped in a protein overcoat. It is in this form that they are most readily detectable. And also, it appears, most active: the naked nucleic acid alone (stripped of its overcoat by delicate chemical means) can produce most of the effects of the whole virus, but it is a thousand times less powerful. Evidently, the researchers suggest, the virus needs to be "carefully packaged for safe transmission." One effective package design is like...