Correction on the correction on Rosalind Franklin. Dr. Novella made the same (very common) mistake for a second week in a row, referring to the technique used to determine the helical structure of DNA as "x-ray crystallography." What you need for a good x-ray diffraction pattern to interpret is an ordered repeating structure - like in a crystal.
The technique actually used was lining up the viscous DNA suspension "fibers" and performing x-ray diffraction photography. Anyone who has messed with a concentrated cell lysate prior to adding DNAse knows how viscous this stuff is, due to the DNA strands. Apparently there's enough regular structure in such a suspension when the fibers are lined up that you can get a decent diffraction pattern, even without the extremely ordered structure of a crystal. This makes sense since DNA is already in a repeating helical structure.
DNA wasn't crystallized until the 1980s. So technically, it wasn't x-ray crystallography - though it used x-ray diffraction (which is used in x-ray crystallography).
Dr. Franklin went on to do pioneering work on Tobacco Mosaic Virus using x-ray crystallography.
