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  • Narrator: From bonnethead sharks

  • to big old Komodo dragons,

  • more than 11 million fluid specimens live

  • in the basement of the Field Museum in Chicago.

  • Josh: There are 883 frogs in here.

  • Narrator: But why hold on to them all?

  • And why keep them wet?

  • Think of it like a library.

  • Stored this way, wet specimens keep their shape

  • and, in some cases, even DNA --

  • basically, the closest researchers can get

  • to keeping a live zoo in their labs.

  • Each jar is a book researchers can crack open

  • and learn from, sometimes discovering

  • brand-new species right here on the shelves.

  • But you can't just drop a Komodo dragon

  • straight into a tank of alcohol.

  • The Field Museum has to acquire

  • and painstakingly prepare them

  • so they can be preserved for centuries to come.

  • The Field Museum acquires its specimens in two ways:

  • either through donations,

  • or sometimes researchers go out in the field

  • to strategically euthanize specimens

  • like this common water snake.

  • If you manage to grab one, they do not hesitate to bite.

  • Narrator: Sara's research relies on new

  • and old specimens to see how changes in habitat

  • have affected the species over time.

  • And the first thing she does with a new one

  • is grab its DNA.

  • This is a fairly new step in the process,

  • since DNA wasn't really used the way it is now

  • until the '90s.

  • It's not impossible,

  • but it is much easier to take tissue samples

  • from fresh animals

  • than it is to take them from preserved animals

  • and get really good results.

  • Narrator: She uses scissors and forceps

  • to collect the DNA sample,

  • first sanitizing them

  • by burning away any random DNA

  • so the results aren't mixed.

  • Sara: It does get so hot, though, that then I have to

  • dip it into some ethanol

  • so that it doesn't, essentially,

  • sear the animal as I work on it.

  • Narrator: Sara takes the sample

  • from the inside of the snake,

  • so she doesn't mess up what it looks like on the outside.

  • Sara: The way I'm cutting is so that

  • if somebody comes along,

  • they're still going to be able to count these scales.

  • Narrator: Plus, that's right around

  • where the liver is located.

  • Sara: And there's the liver! Right there.

  • Narrator: It's Sara's favorite tissue to collect

  • for DNA extraction because it dissolves easily.

  • Sara: It turns everything pink.

  • It says "SR 1291."

  • I double-check my tag is "SR 1291."

  • Narrator: Then the DNA goes into

  • these massive liquid-nitrogen freezers

  • with thousands of other DNA samples.

  • Now she's ready for formalin,

  • the liquid that preserves the tissue

  • and keeps a specimen frozen in time.

  • It's sort of like embalming it,

  • just like a person at a funeral home.

  • Narrator: Sara has to keep in mind what info she needs now

  • and what researchers might need in the future,

  • like the sex of the snake.

  • Sara: It's always good to see if,

  • maybe if it's a male snake,

  • if you can find the hemipenes and pop them out.

  • Narrator: Sara will pose the snake

  • so you can see the visible penises

  • from outside the jar without even opening it.

  • And this pose is how it will stay

  • for the rest of its afterlife.

  • The coil doesn't just look snaky ...

  • Sara: There is some art to it.

  • And you can stack lots and lots of them

  • on top of each other in a jar.

  • One,

  • two,

  • three, four.

  • I've got five snakes here,

  • and there's another, probably, six in this jar.

  • Narrator: Last step in this part of the process

  • is tucking it in under a formalin-soaked paper towel.

  • It keeps the snake saturated

  • without having to fill the tub.

  • Sara: Good night, snaky.

  • Narrator: Over a few days,

  • the formalin will set into the tissue,

  • leaving the snake fixed in place.

  • Almost like you're holding a rubber snake.

  • Narrator: Larger animals might need more

  • than a few injections,

  • like this catfish Caleb is working on.

  • Calculating the amount of formalin needed

  • is mostly based on experience and feel.

  • Too little, and your specimen will start to decay

  • and get floppy.

  • Too much, and your specimen will bloat

  • and become disfigured.

  • Caleb: You don't want to make the belly do this

  • because you've pumped it with so much formalin.

  • Narrator: Once Caleb is confident his catfish

  • is sufficiently full,

  • he'll move it into a tank of even more formalin

  • to soak for about a week.

  • Caleb: We're going to add a bit of cheesecloth

  • just to make sure that no parts of it

  • are sitting outside of the formalin.

  • Narrator: After the formalin, the team switches over

  • to alcohol baths for long-term preservation,

  • like with this Komodo dragon.

  • The alcohol is less toxic than formalin,

  • so it's safer for researchers in the long run,

  • and the specimen doesn't change much

  • while it sits in its final resting tank,

  • just the color of the liquid.

  • Josh: Especially large specimens,

  • they'll release a lot of debris and fatty oils

  • that were stored in their body,

  • and it'll leech out into the ethanol,

  • and that causes a lot of the discoloration.

  • It's still doing its job

  • and keeping the animal preserved.

  • Narrator: Most specimens in the wet collection

  • are kept looking as lifelike as possible.

  • But others ...

  • Caleb: We can clear away all of the tissue,

  • stain the bones and stain the cartilage,

  • and we can end up with just a skeleton

  • that we can put under a microscope.

  • Narrator: Extra-small fish have extra-small bones

  • that are difficult to keep track of.

  • So instead of isolating the skeleton,

  • this method keeps it contained

  • but visible inside the body.

  • First step is dyeing the specimen blue.

  • This specific blue dye is attracted to cartilage,

  • and the red dye clings to calcium.

  • A few days for each is typically enough to lock in the dye.

  • The next step is to clear the fish.

  • We use an enzyme called trypsin

  • that digests proteins and break them down,

  • but it leaves the collagen

  • that holds everything together.

  • Narrator: Making the fish completely see-through.

  • Finally, he dyes the bones red.

  • Caleb: One of the advantages of clearing the fish

  • and then putting it into the red dye

  • is you can keep an eye on it

  • to see how dark it's getting.

  • Narrator: The whole process can run a few days

  • to around a month.

  • Done right, and your final product

  • are these almost alien-looking specimens.

  • Caleb: It's kind of like Jell-O,

  • and you store it in glycerin in the end,

  • because glycerin and collagen

  • have the same refractive index,

  • or the way that light passes through.

  • Narrator: These specimens go right into collections

  • alongside all the opaque ones,

  • so researchers can access them

  • when all they want to see is bones and cartilage.

  • Caleb: You can put this under a microscope.

  • You can move bones around

  • and see how one bone moving

  • affects other bones nearby.

  • Narrator: Entirely new species

  • have been discovered this way,

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