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,
like these two fish species
that are identical on the outside.
Caleb: But when you clear and stain them
and you look at their bones,
you can actually see that there are differences
in their skeletons between species.
Narrator: New species can hide on the shelves for decades.
Sara: So, here we go.
Narrator: Like this spider-tailed horned viper
kept under lock and key.
It was originally collected in the 1960s,
and researchers first thought it was
a different species of viper with an abnormality.
Sara: This weird, weird parasite or a tumor.
Narrator: But then ...
Sara: In the early 2000s,
some herpetologists came along,
and they said,
"You know, I think it's a whole new species altogether."
Narrator: Once a second one was found,
they compared it to this one.
Sara: And the species Pseudocerastes urarachnoides
was described from this very individual,
this holotype.
Narrator: But specimens like this one
are only helpful if you can find them.
Caleb: It's kind of like a library,
but jars of fish.
Different families of fishes have numbers,
and then within each family,
they're arranged alphabetically by genus
and then by species.
Narrator: There's even a field in the database
for noting when and where a specimen was last seen.
Caleb: So if someone asks for it, we know that,
well, at least at this date,
it was spotted on the shelf in the collection.
Narrator: And once you find it,
it's not always as simple as pulling a jar off a shelf.
Josh: There are 883 frogs in here.
Narrator: And each one has its own ID number,
so if a researcher wants to look at a specific frog ...
Josh: I have to sit here and just pick each one up
one by one and be like, "Nope, not this one.
"Nope, not this one," until you find the right one.
Narrator: These frogs used to be stored separately,
but at times ...
Josh: We've definitely run out of space.
They combined jars of the same species
but collected by different people,
collected from different places,
collected at different times,
but then you end up with the same problem I mentioned here.
Narrator: Getting rid of stuff is not an option.
Old specimens can be especially valuable.
Josh: This is the oldest specimen we have
in the amphibian and reptile collection.
Narrator: Sara has even developed a technique
for recovering DNA stuck inside them.
The process is similar to getting DNA from fresh tissue,
with a little extra work.
Sara: That extra work includes heating it up real high
and trying to digest it
and pull the DNA away from the formalin
over a much longer period of time.
Narrator: But it can be hit-or-miss.
It could be anywhere between 0% success
all the way up to, like, maybe 60% or 70% success.
If all you have is a 100-year-old snake in a jar,
you might as well give it a shot.
Narrator: Like library books,
some of these jars can sit untouched
on their shelves for years.
But all it takes is a curious person to crack one open,
and our understanding of the natural world
can completely change.
Sara: I always think whether it's DNA,
whether it's taking the whole specimen to preserve,
this thing then didn't just die in vain.
It lives on in science forever.