PCR blew a gigantic hole in science, as my teacher used to say, in the early 1980s. Basically youve got enzymes that replicate your DNA when your cells divide. So does every cellular organism. PCR uses these enzymes, harvested from bacteria, to replicate DNA in a test tube. Before this was invented, you really couldnt do a darn thing with DNA, or anyway almost nothing. Now you do everything. Its one of history's greatest inventions. This weird, kind of cool dude Kary Mullis invented it, sort of, or at least was the first to figure out how to get 'er done in fine, and then the first to really do it. The thing is, he's actually an idiot.
Suppose there was reason to suspect the presence of some kind of organism in your bloodstream, a taco for instance. You must have fallen down on top of it and stabbed your shoulder with a shard of the shell, thats the only way this could happen. Thereupon, with your permission, I would use PCR to make billions of copies of a certain fairly short sequence of cow DNA present in your blood. I would mix this product with ethidum bromide which sticks in the DNA and fluoresces under UV light so I can see the stuff. I would run this out on a gel in an electric field, which would show rather precisely whether it is of the expected size. I would look up the sequence that is expected, and use bacterial restriction enzymes that cut DNA in half only a certain sequence, eg AAGTTGAA, that I expect to be present. I would run it out again to see if the cut fragments were the correct size. At this point you would be considered cow-positive, or cow-negative as the case may be, and I would make sure to record in my notebook. But it honestly wouldnt work at all if you simmered the beef thoroughly, which I surely hope you did. The thing is I would probably be almost done running the test before I thought of that, not to mention that I forgot to ask if the taco was beef or chicken. Lamb, wow, are you serious? You must have a damn sight more dough than Ive got.