ANATOMY OF A P H ENOMENON But so little is really known about the existing local phys ical conditions, which may differ considerably from those predicted by our present "models," that no simple answer can be given to any question about the path life could have followed on that planet. A considerable change is perceptible today in the ideas entertained by biologists dealing with the forms of life that may survive in environments very different from ours. Exper iments realized since 1960 tend to show that the early con cepts that made oxygen a necessary element for life were exaggerated to a large extent. Cucumber seedlings raised in only two percent oxygen { vs. 21% in our air) can be frozen for an hour and then thawed without dying: This is but one of the experiments made by Dr. Sanford Siegel of Union Carbide Research Laboratories that led him to the discovery that high forms of plant-life such as beans, could survive well in environments generally considered as extreme, and that low oxygen content of the atmosphere actually im proved resistance to freezing. In the same series of experiments, it was found that cac tus grew in subzero cold when the oxygen content of the atmosphere was reduced to 0.05% and that turtles remained normally active when the atmosphere was reduced to a tenth of normal sea-level pressure. When he simulated a Jupiter-type atmosphere-ammonia, methane, and hydrogen-the same author found that some bacteria were very happy in this mixture. Most exobiolo gists consider that water is essential to life, and water exists on Mars, although not in abundant quantity. But some specialists in plant physiology, such as Dr. Frank Salis bury, consider that certain forms of life could use water as a vitamin rather than as a basic constituent, and would thus require only infinitesimal amounts of water in order to survive. These ideas show a considerable departure from the traditional conceptions on the possibility of finding life on other planets, in our solar system and elsewhere.
METEOR I TES Meteorites are the only physical evidence we possess on which research of living organisms such as germs or microbes of extra-terrestrial origin might be attempted in the labora tory. According to a report by C. Meunier, Pasteur tried to 68 .