In 1871 Lord Kelvin, when president of the British Association, suggested that the origin of life as we know it may have been extra-terrestrial, and due to the "moss-grown fragments from the ruins of another world," which reached the earth as meteorites. It was objected to this that the extreme cold–very near to the absolute zero–which prevails in interstellar space would be fatal to all germs of life carried by such meteoric stones. But twenty years later Sir James Dewar showed that this objection did not hold, since at any rate some forms of life–certain bacteria–could survive an exposure of several days to a temperature approaching the absolute zero. Later Sir James made some very striking experiments by exposing cultivations of phosphorescent bacteria to the temperature of liquid hydrogen (252 degrees below zero centigrade). These bacteria may be obtained by selective cultivation from sea-water taken on the coast, in which a few are always scattered. A rich growth of these bacteria in gelatine broth gives off a brilliant greenish light when shaken with atmospheric air or otherwise exposed to oxygen. The light is so intense that a glass flask holding a pint of the cultivation gives off sufficient light to enable one to read in an otherwise dark room. The emission of light is dependent on the chemical activity of the living bacteria in the presence of oxygen. In the absence of free oxygen they cease to be luminous. As soon as they are killed the light ceases. When they are frozen solid the light ceases, even in the presence of free oxygen gas. When a film consisting of such a culture is frozen solid it will remain inactive if the low temperature be maintained for months, though exposed to free oxygen gas, and then, as soon as it is liquefied by a gentle rise in temperature, the active changes recommence, and the phosphorescent light beams forth. Sir James Dewar exposed such films to the low temperature of liquid hydrogen for (so far as I remember) six months, and obtained from them at once the evidence of their living chemical activity, namely, their "phosphorescence," as soon as they were thawed. In the frozen state, at a temperature of minus 250 degrees centigrade, nothing, it appeared, could injure these phosphorescent bacteria. No chemical can "get at them" at that temperature, the most biting acid, the most caustic alkali cannot touch them when, like them, it is in a hard, solid condition. Powdering the film by mechanical pressure has no effect on the bacteria. They are too small to be crushed by any mill. Such germs would, it seemed, surely be able to travel through interstellar space, as suggested by Kelvin.