y after my return to Europe, I took up the subject of
longevity, as to which Giessler had collected much curious information,
and formed certain theories, one being that people of sound constitution
and strong vitality, with no hereditary predisposition to disease may, by
observing a correct regimen, easily live to be a hundred, preserving until
that age their faculties virtually intact--in other words, only begin to
be old at a hundred. So far I agree with him, but as to what constituted a
"correct regimen" we differed. He held that the life most conducive to
length of years was that of the scholar--his own, in fact--regular,
uneventful, reflective, and sedentary. I, on the other hand, thought that
the man who passed much of his time in the open air, moving about and
using his limbs, would live the longer--other things being equal, and
assuming that both observed the accepted rules of health.

The result of our discussion was a friendly wager. "You try your way; I
will try mine," said Giessler, "and we will see who lives the longer--at
any rate, the survivor will. The survivor must also publish an account of
his system, _pour encourageur les autres_."

As we were of the same age, equally sound in constitution and strong in
physique, and not greatly dissimilar in temperament, I accepted the
challenge. The competition is still going on. Every New Year's day we
write each other a letter, always in the same words, which both answers
and asks the same questions: "Still alive?" If either fails to receive his
letter at the specified time, he will presume that the other is _hors de
combat_, if not dead, and make further inquiry. But I think I shall win.
Three years ago I met Giessler at the meeting of the British Association,
and, though he denied it, he was palpably aging. His shoulders were bent,
his hearing and eye-sight failing, and the _area senilis_ was very
strongly marked, while I--am what you see.

I have, however, had an advantage over the professor, which it is only
fair to mention. In my wanderings I have always taken occasion, when
opportunity offered, to observe the habits of tribes who are remarkable
for longevity. None are more remarkable in this respect than the
Callavayas of the Andes, and I satisfied myself that they do really live
long, though perhaps not so long as some of them say. Now, these people
are herbalists, and when they reach middle age make a practice of drinking
a decoction which, as they beli