rough
the late 1900s refinements continued to be made, but it wasn't until
1988 that the fathers of replacive surgery, Doctors Mills, Levinson
and McCarty made the breakthrough that revolutionized the whole
concept. In very simplified language they unlocked the key to
producing specialized living tissue through a bombardment of an
extremely complex carbon compound with amino acids and electricity,
then making it selective in function by a fantastically intricate
application of radiation.

"That pulmonary replacement you received in 1991 was undoubtedly one
of the first successes. You were quite lucky, you know. Up until 2017,
only about five per cent of their synthesized hearts lasted more than
thirty days. At any rate, the principle was established, and it was
proven that it could work. Most of our work from then till a few years
ago has been in improving and refining the work those three good
doctors did over three hundred years ago."

Letzmiller's cigar had gone out, and he discarded it in favor of a
cigarette. "That would be the end of my history lecture, if it were
not for the nature of your trouble."

Lee looked at him closely. "Why's that?"

"Well, Mr. Lee, the big thing missing in that summation is the
seemingly impossible task of synthesizing nerve tissue, especially
that of the cerebral cortex. It's been approximated, at any rate
closely enough to give us good enough results to allow an artificial
tissue to respond to brain signals about ninety-eight per cent as well
as the original would. But actual duplication? No. At least not until
about three years ago. To tell you the truth, it is barely out of the
experimental stage."

"Experimental!"

* * * * *

"Yes, this will be the first complete replacement of a human brain.
Oh, of course it has been done with animals, and it has been
successful with partial replacements on humans. But you will have the
honor of being the first human with a complete substitution."

Lee could not contain himself. "Doc, that's just it! There won't be a
single atom of me except what you fellows have conjured up--"

Letzmiller broke in mildly. "I think 'conjured' is hardly the proper
word, Mr. Lee."

"Well, of course, I didn't mean that. But don't you see what I'm
driving at? You could just as well start from scratch and duplicate me
without bothering about going about it piecemeal. And what does that
make me?"

The doctor had been looking