What differ?

There's all sorts of things I don't care about in my teaching practice at The Institute.  I don't care how the students spell, so long as there in no confusion about what is meant. You wouldn't want to confuse Fabry's disease with Farber's disease, the causes and treatment are radically different. I'm not pushed about putting the date on the left or right side of a lab write-up. I don't expect complete attention and deathly silence when I lecture. otoh, I'm here on the planet and at The Institute to convey a certain passion for science and to encourage younger people to polish their crap-detectors. If it says X in The Book, then let's at least see what happens if we try Y. Then we'll have a much more direct appreciation of how important X is [not?].

On The Blob and in many of my classes, I'll have a rant about spurious accuracy, as when students report a result for the estimated diameter of cell as 28.56 micrometers because that's what it says on their calculator. By writing the trailing 6, you are asserting that a cell is not 28.4 or 29.1 microns across because you can measure it with more accuracy . . . and that's just nonsense because when you apply the micrometer screw gauge, you'll squidge in the cell membrane. Heisenberg, of course, had a lot to say about this with his Uncertainty Principle.

We had an interesting [but potentially mind-numbingly boring] practical last week in Yr1 Cell Biology, where we were comparing a typical plant cell [the slippy epidermis between the layers of an onion is one cell thick] with a typical animal cell [a swab of the inside of a cheek yields a good gobbet of human epidermal cells and occasionally some rasher and toast from breakfast]. No, it's not original to us; generations of biologists have been raised on this practical [see image R]. Yes, it's the same practical which provided a lever for a sermon on plagiarism 3 years ago.  But we've made progress this year: it is no longer a requirement to print out and sign a Plagiarism Document with every shaggin' piece of submitted work. This policy change will save many trees and get students to think about what constitutes plagiarism.  Anyway, the protocol in the Cell Biology Manual says that human cheek cells must be stained with methylene blue, while the onion cells should be stained with iodine. Why? IF there was starch present in the onion epidermis, THEN iodine stains the grains blue BUT there isn't. I am re-writing the manual today so that everyone makes three preps of the 2 materials one stained with methylene blue, one with iodine and one left unstained. THEN we'll know which stain works best, and we may be able to stream-line the protocol.

Last week was also momentous because the 20 week module on Food and Fermentation Microbiology aka F&F kicked in. I've had one lab section for this course for 3-4 years now and after the first year of teaching from ancient handouts, I typed the whole thing up as a F&F Manual in Six Chapters. It can now be amended and editted and extended without looking tacky with hand-written changes and additions. But I slavishly copied most of the words from the original handouts. This year I requested and required the students to follow the Manual when making up media to pour into Petri dishes BUT to note any differences between what I'd written and what was written on the side of the plastic bottle of ingredients. With some theatre, I then picked up a bottle of media and asked why it instructed to weight out 28g of powder for each litre of water. Blank looks, to which I triumphantly announced that 28g is an [old-fashioned, imperial] ounce and that suggested that it was equivalent to a table-spoon. It didn't matter-a-damn whether they put in 30g and 25g might even work. In other words they were not to piffle about weighing out 28.0000g of powder while there was a queue waiting for the access to the balance. Note: 25g might not be enough to make the agar set, so it's a trade-off between saving 10% on the media bills versus having something that you can streak bacteria on.

I was delighted to see in the write-ups that my [robotically copied tsk!] ingredient list for "Baird-Parker Agar" differed from what the kids actually used.

Ingredient	Manual	LabM	Merck
Tryptone	10g	10g	Peptone 10g
Lab Lemco	5g	Beef Extr 7.5g	Meat Extr 5g
Yeast Extr	1g	1g	1g
Na pyruvate	10g	10g	10g
Glycine	12g	12g	12g
LiCl	5g	5g	5g
Egg yolk emuls	50ml	50ml	50ml
K tellurite 3.5%	3ml	4ml	4ml
Agar	20g	20g	15g

That will give me something to rant about at the next class [b'golly, that would be at 1400hrs today, how time flies]: Tryptone? Peptone? Schmeptone? what does it matter, so long as a boy loves his mother there is some generic protein in there. This comparison also tells us that 25g of media is probably enough to pour a solid plate, because Merck's recipe has only 75% as much agar as the other two sources.
Q. How long is a piece of string?
A. As long as it takes to tie a knot.