An old rat is like a senile old man; he is bald and emaciated, his eyes are clouded, his breathing is labored. He stays in one place, with bent back, and has small interest in anything. If you cut one of his genital ducts, however, which is a comparatively slight operation, it has the effect of making the interstitial cells multiply actively. Waves of life flood his being. Within a few weeks he is transformed. These currents restore and rebuild him; skin, muscle and mind. Both in looks and behavior he is indistinguishable from other strong rats. He has cast off old age. Senility, which sets in with men when they are from sixty to eighty years old, begins after twenty to thirty months in a rat. He is then about through. But when an operation is performed on a senile rat he gets from six to eight months' new life. In other words, the addition to his normal span is 20 to 30 per cent. That would be a large fraction of life for a man to live over again. The rat lives it vigorously, eagerly, back in his prime. When senility again comes upon him it is in a modified form. His organism as a whole is in better shape. It is his mind now that tires. As Steinach has already cut one or both of his genital ducts, that method of stimulating his cells cannot, of course, be repeated. But another operation is ready. Some unfortunate young male is deprived of his testes by Steinach, and these are implanted forthwith in this hoary old rat. A second spell of active life follows, not so long as the first. It ends in acute psychic senility. The rat goes all to pieces. It is as if the brain, twice restimulated to emotion, curiosity, keenness, had approached the very limit of its running, and was completely exhausted. Steinach has not yet tried whether a third rejuvenation is possible. That remains to be seen. He lives in Vienna, and everything there has come to a stop. He has no assistants, no funds, with which to conduct further experiments. "May happier lands or cities carry the work on," he writes at the end. It seems as though some rich American ought to stake the old boy. * * * * Steinach has naturally found it more difficult to give new youth to females. But here, too, he has in a measure succeeded. X-ray treatment and ovarian transplantation are the methods employed. As to human experiments, there is a colleague of Steinach's named Lichtenstern, who has operated on numerous men and women with apparent success. There has not been time yet to measure how long their new lease of life is to be; but they have regained the joy of life they had lost--strength and powers of work. Still, all this needs confirming.