Math?

By David Lumelsky

For the first couple weeks of phage lab, it was just following the instructions in our lab manual and using a little intuition. We were still learning how to practice all the laboratory techniques we needed, and the hardest part, at least for me, was trying to figure out which micropipette to use. We all quickly caught on about how to plate using aseptic technique, how streaking worked, how to do a serial dilution and any number of things that occur in a biology laboratory. Essentially, phage lab was turning out to be everything I wanted it to be. This was no intro chem lab where significant figures have become the bane of my existence. I was seeing real results without doing all that much calculation, save multiplying by 10-1 every once in a while.

Then we got a medium titer lysate. Exciting as that may be, then we had to calculate its titer and figure out how much of it we would need and at what dilution to create a web plate. Unfortunately for me, that involved a lot of math. Math may not be my strong suit, but I forged ahead and managed to plate…something. That something turned out to be off by some ridiculous factor. There were so few phages in the dilution that I made, that there wasn’t a single plaque on any of my plates, including 4x plate with 4 times the quantity of phage that I would theoretically need to make my web plate. So I went back and looked at my lab notebook and I noticed that I had done my dilution all wrong. This wasn’t going to work.

So, the next class I went through the entire procedure until I finally figured out what I had to serially dilute to and how much of that dilution I would need to plate. I thought I had figured everything out, it all made sense to me. I plated these quantities and left phage lab that day happy with my progress only to return the next day and find that I was off by a factor of ten. How on earth did I manage that?

I went through every single calculation I did, the titer, the size of the plate, the area of the plaques, how many pfu I would need to cover a plate etc. and lo a behold: I moved a decimal point. Just one little dot had messed everything up and now I had to redo the empirical test for a 3rd time. At first this seemed disheartening, but actually, it was one of the most valuable experiences I’ve had in phage lab.

Things don’t always go right in a laboratory, and when they don’t you have to troubleshoot. Apparently, I can’t do math, but that doesn’t mean I can’t work through it and eventually figure it out for myself. Moreover, when I took my plates out next class and I did indeed have a web plate, it was one of the most gratifying feelings that I could have. Though this is far from real rigorous research, this little experience in phage has definitely made me a better scientist, and perhaps, a little more careful with my decimal points.

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