Re: How was the Krebs cycle discovered (what did the experiment look like)?

There was no single experiment or even a short series of experiments that
led to the formulation of the Krebs/citric acid cycle.  It was a lot of
laboratories over many years that led to Krebs' 1937 paper first proposing
the cycle.  Krebs certainly contributed experimental work in addition, but
so did many other labs over many years.  Krebs contribution was in
significant part the recognition that the data suggested a catalytic cycle
in which only small amounts of the substrates were needed since the
intermediates could be regenerated.  That is, it was a circle or a cycle of
reactions.

The following link give the biography of Sir Hans Krebs that is posted on
the Nobel Foundation's website.  On that page is a link to a pdf file of
Krebs' Nobel lecture.  It's as good a history of the discovery as I know
of.  In fact, Krebs clearly downplays his own role and credits many other
people with various discoveries.
 http://
nobelprize.org/medicine/laureates/1953/krebs-bio.html

The following are links to animations and/or explanations of the
Krebs/citric acid cycle.
 http://www.johnkyrk.com/krebs.html
 
http://www.science.smith.edu/departments/Biology/Bio231/krebs.html