ull accounts of his work were published last summer in the
great biological journal founded by Roux, and these were summarized and
discussed by the London +Athenaeum+, which is now the most interesting
of all English weeklies. It is from the +Athenaeum's+ account that I am
taking these facts.

Steinach has been studying the interstitial cells that fill in the
spaces between the tubules of the testes, in males, and between the
follicles of the ovaries in females. His reason for choosing these cells
for his experiments is that they are a well-spring of life. Furthermore,
since all our vital functions are interrelated, to make these cells
active gives the whole organism new life and strength. This is not the
only way of stimulating the organism, but it seems the most powerful.

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