About 15 years ago I read Haing S. Ngor's autobiography "A Cambodian
Odyssey."  My recollection of some of the details is incomplete now. 
I recall that he wrote about suffering from some malady--dysentery,
perhaps?--that would have been fatal, but that his wife got hold of a
yam and cooked it until it was essentially carbon, and that eating it
saved his life.

I may be recounting the facts incorrectly, but this is the way I remember them.

Haing Ngor was a doctor in Phnom Penh before the Khmer Rouge drove
everyone out to the countryside to work as slaves of Communism.  He
knew what was wrong with him and what would help his condition.

I would like to know what it was that the yam did for him and why it
had to be cooked to death so it would help.  Why a yam, in particular?
 Does a yam have some special properties against disease, or would any
other fire-blackened vegetable have had the necessary effect?

Thank you,
Archae0pteryx

Wild yams do have medicinal properties:

"Medicinal Action and Uses---Antispasmodic. Perhaps the best relief
and promptest cure for bilious colic, especially helpful in the nausea
of pregnant women. Valuable also in painful cholera morbus with
cramps, neuralgic affections, spasmodic hiccough and spasmodic
asthma."

http://www.botanical.com/botanical/mgmh/y/yam---01.html

I could not find anything that described cooking yams for curative
purposes, but here's a reference to the blackening of herbs in Chinese
medicine:

"Whenever scales are used, the weight given is always that of the herb
before any stir-frying which may be specified on the prescription. The
herbs may be fried in honey, water or rice wine, or `burned` until
black in a red-hot wok."

http://appft1.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.html&r=43&f=G&l=50&d=PG01&s1=Compositions+for+removal+of+toxins

hi archae0pteryx!
keep in mind that there are many different kinds of yams, and some
from Asia are quite different than the bright orange ones we eat at
Thanksgiving. I know of someone who grows oriental yams and feels that
they have special healing properties (what exactly I'm not sure); but
he's mostly impressed that they just grow and grow and grow, year
after year, without much need for care.
I could find out for you if you like; and I could ask him if he burns
his to a crisp (!)  I doubt it . . .

ts

Hi, Pink and ts, and thank you for your comments.

From what I recall of the account in the book, the author asked for
the yam to be overcooked not because he wanted to eat it that way but
because that was what it took--maybe acting as some kind of
filter?--to clear out whatever it was that ailed him.  I'm pretty sure
it was a gastrointestinal affliction.  I would not think a person
would do that otherwise.

As I remember it, his wife sacrificed her yam to save him.  Everyone
was starving, and people would scrabble in the dirt for a few grains
of rice.  This was a very big act of love.

I thought there was some connection between the specific ailment and
the use of a carbonized yam as a treatment.  I'm looking for an answer
not only to what the yam might do but to what the illness was.

Tryx

Maybe he was poisoned and the yam was somehow converted to activated
charcoal?  (Seems unlikely under normal cooking conditions, but who
knows.)

http://www.ilpi.com/msds/ref/activatedcharcoal.html