In all your years of schooling, you have learned many facts, but rarely how we know those facts. While facts often cannot be applied to other situations, method frequently can be adapted to solve future problems. Here is another of those methods - of the Nobel class.

    Mary Lou and Jimmy slinked forlornly out from the meeting hall and onto the verandah which sat atop towering cliffs overlooking the ocean. Crushed, Jimmy stood off at a distance, while Mary Lou at first looked over the low rock wall and watched her tears fall and disappear to be dashed upon the distant rocks far below. She moved to sit on the wall and swung her legs over contemplating sending her whole self dashing upon the rocks just as those tears had also been dashed - to say nothing of her future happiness. Just then her mother poked her head out the door: "Oh, there you two are," she said happily. "You should be inside helping your brother; your work has attracted quite a big crowd," she continued before seeing tears. "Oh, oh! Do I sense that you two had a spat? You'll have to tell me about it later, I'm late - I've got to run off to meet my sister."

    "But, Mom, isn't Jimmy's mom your sister?" choked out Mary Lou.

   "Well, yes, sort of-: she's my sorority sister. Gotta run now. Life is full of hard knocks. I'm sure things will work out between you both."

    Inside normally talkative Jason stood dumb in the presence of Cheryl, but Wilbie began stealing the show right after Cheryl sought help from her colleagues in explaining what ideas initiated this whole endeavor. Wilbie, wearing what seemed like clean and even pressed overalls for this special occasion, explained that they needed to find a second way to prove last year's results regarding their Bundling Board Experiment. However his mention of that term immediately diverted his audience's attention as they wanted to know what a bundling board was. So he told them that when a colonial New England family was visited by a potential beau for their daughter, the parents were at first perplexed about where he was to sleep that night since the house had only one bed. Dad then got the idea of setting a wide wooden plank on edge between the visitor and their daughter so that no hanky-panky could transpire while all were bundled in bed for the night. "In a way, a bundling board prevents physical contact between the young couple or between the two types of bacteria we were using. This, yet allowing for whispers or growth medium to pass between them," Wilbie concluded. "But back to the point," he motioned onwards.

    "We wanted to tag protein, and nucleic acid with something that was unique to each of them. But what? Obviously using C-14 wouldn't work as both have lots of carbon in them. Jason, here, and I were sitting waiting for the school bus when it suddenly hit us - DNA and RNA never ever have an sulfur atoms in them, but protein does - you know, in the amino acids methionine and cysteine, so that let us think about using the radioisotope S-35. But next what about the nucleic acids? Can't us P-32 because a lot of proteins are activated by the addition of phosphates. All we had left was C, H, N, and O - but those are all common to proteins also."

    "My uncle, Dr. Sørensen at Syntech, reminded me of our previous use of using thymidine that is labelled with H-3, tritium, among the hydrogen atom surrounding the C in its '5-methyl' position. 'That should work well,' he advised, 'At least for tagging DNA.' So, you see, we were now somewhat resticted to DNA and protein, and had to give up on RNA tagging."

    Finally Cheryl found her voice. "We took a growing culture of E. coli, and then added three things simultaneously to it - enough T4 to infect at least 95% of the cells, some of Sørensen's tritiated-thymidine, and some S-35-sulfate. We waited for 30 minutes to give time for the phages to infect and reproduce themselves, and then burst their host cells releasing lots and lots of progeny phage - each with S-35 in their capsid proteins and tritium in their DNA."

    "Then we used differential centrifugation to separate the intact virions from all the other stuff in the culture - the unifected cells, and the burst-cell debris," Wilbie interjected, pointing to one of the diagrams showing how a virion was radioisotopically labelled - red where the S-35 was located and blue where the tritium, the H-3, would be.

    One of the onlookers looked puzzled. "How can you tell one isotope apart from the other? Help me to understand, please."

    By this time Jason came to and knew he had to be man enough to impress Cheryl, so he started talking, but was immediately interrupted by someone's asking what tritium was. "Ordinary hydrogen atoms have an atomic weight of 1 because there is only a proton in the nucleus. Deuterium - 'deuter' means two - is a heavier isotop of hydrogen: it has a proton and one neutron in its nucleus, and it is not radioactive. But if there are two neutrons in the nucleus along with the one proton - three things - TRI-tium, you have a radioactive situation. Understand, now?"

    "Back to the question - telling tritium from S-35. When radiactive neutrons disintegrate into a proton and a high speed electron called a beta-particle, those disintegrations are of different explosive energies characteristic of the particular element involved. In the case of tritium, the power is rather small, but for S-35, well, it's about 10-times stronger.

    "Now I can hear you thinking how can we detect a low-energy beta from a high-energy beta? We have radiation detectors such as Geiger counters and Scintillation counters - both give off a spark or twinkle when hit by beta particles. Strong betas make a brighter spark or twinkle than do weak betas. So we build in electronic eyes that count bright and dim twinkles. Understand, now?"

    Wilbie, standing at the side, could see that Cheryl herself finally understood something of all the nuclear physics. Jason had won some points with Cheryl, who now picked up the presentation as it was evident that now was the time for her to talk biology, a field she understood very well.

    "We took another non-radioactive culture of E. coli, and dumped in some of our doubly-labelled T4. We took samples every minute, and put those samples in a blender hoping that the turbulence would be able to rip the T4 off of the bacterial cell surfaces. After centrifuging down the cells - the ripped-off phages was too small to centrifuge down easily, we tested the overlying supernates and the cellular pellets at the bottom of the tubes for which isotopes were present." And she pointed to their graph in a manner which would leave even Marla M. envious.

    What does this graph show, and, more importantly, what does it corroborate?

    We've dwelled a bit on radiology these past few ML-quizzes. Most of you will encounter more and more of this in future years of practicing the giving of therapy, and trying to help patients understand what is happening to them.