794 MAN'S PHYSICAL WELFARE ested in controlling the combinations of genes in chromosomes, while the physical scientist speculates about the control of living organisms by the use of the same chemical that the genes produce. The study of the chemistry of the genes is very difficult, but it is vital to an understanding of the nature of life and increased control over living organisms. Is it possible that character might be made to order by the use of chemicals in the future? If so, what kind of character will be desired? This is a question of values again. Do Viruses Represent a Transition between Living and Nonliving Matter? Viruses are so small that they pass through filters which retain bacteria and are, therefore, called filterable viruses. Viruses cause infantile paralysis, encephalitis, rabies, mumps, smallpox, trench fever, measles, yellow fever, hoof and mouth disease, psittacosis, and probably influenza and the common cold. Fi(.. 321. Toljacco Mosaic Virus and Anti-T.M.V'. rabbit serum. Magnification, 40,000: 1 by electron microscope. (Courtesy of Thomas F. Anderson. RCA Manufacturing Company.) It is known that virus disease may be spread by contact or even by breathing the air containing droplets of moisture resulting from coughing and sneezing. Such virus diseases as dengue fever, yellow fever, and sandfly fever are transmitted by mosquitoes and flies. A step in the conquest of virus diseases was made in the recent discovery that sodium sulfanilyl sulfanilate is effective in curing distemper in cats and dogs. Distemper is a virus disease somewhat similar to human influenza.
PROTOPLASMIC AND CELLULAR ORGANIZATION 795 Viruses are enemies of all plant and animal life. In some respects viruses appear to be living organisms, and yet the pure substance separated from the virus disease of tobacco, the tobacco mosaic, has the property of causing this disease. A pure virus appears to be nothing more or less than a protein molecule, but, unlike the proteins of foods, it reproduces itself as do living organisms. One theory is that viruses behave catalytically like enzymes, causing molecules which are replicas of their own structure to be synthesized in the host. Perhaps viruses represent the transition between living and nonliving matter. STUDY QUESTIONS 1. What has modern Science learned about the nature of life? 2. What are some of the lines of exploration now open to the biochemist? 3. Describe Carrel's experiments. 4. Why is Charles Lindbergh's diffusion pump important? 5. To what extent, and how, has modern Science increased the life-expectancy? 6. Describe the experiments with the single-celled plants of the genus Chlamydomonas. 7. Explain the mechanism by which colchicine produces new varieties of plants. 8. What are the modern versions of the "philosopher's stone" and the "elixir of of life" or "the fountain of youth"?