become concentrated
into the desire for a little food, and immobility. If now, something
is done to his sex apparatus, a marvelous transformation may be
effected. That something no one could predict. It consists in slitting
the genital duct, which leads from the germinal cells to the exterior.
After the operation, the germinal cells, which grow into the
spermatozoa, atrophy and disappear, since they can no longer function.
As if released from some restraint, the interstitial cells, however,
multiply enormously. With their multiplication, the miracle of
rejuvenation is performed.

After some weeks the sluggish currents of being in the rat, which had
slowed down as a preliminary to stopping altogether, flow fast and
furious. Waves of new chemical substances inundate his cells. And they
respond like the fields that border the Nile after the annual flood.
All his tissues, skin, muscle, nerve, even bone, are restored. A
vitality is created which makes him bound and dart like a youth of his
species. In due time, though, senility returns. It is as if a storage
battery, recharged, runs down and becomes dead again. Slitting the
genital duct of the other testis, causing its interstitial cells to
hypertrophy and multiply, repeats the effects of the first experiment.
The organism responds again to the new waves of vitality that vibrate
through it. That it is recharged is demonstrated again by a revival of
sex appetite and sex activity. The female which had become an object
of indifference is reinstated as a creature to be sought and pursued.
The second period ends in its turn. And now entirely new interstitial
glands, in the form of fresh testes removed from a young animal, are
transplanted into the body of the old rat. Once more youth returns.
But now it burns itself more quickly than even before. An acute
exhaustion of the mind appears first. Then all the other phenomena of
old age steal back upon the old rat, and senility, firmly established
in the saddle, rides him to the end.

THE POSSIBILITIES OF REJUVENATION

Whatever other deductions may be extracted from these experiments,
they prove beyond a doubt the existence of an endocrine factor in the
process of aging, as well as an arterial. They also demonstrate that
the internal secretion of the sex glands, well advertised as it has
been as the Elixir of Youth that Ponce de Leon, and Brown-Sequard with
so many others, pursued in vain, is not the whole story. For if it
was, th