The first time I worked with rodents, I was a high school student doing a neuroscience research project at the University of South Alabama. In order to get clear brain histology, we had to perfuse the animals with saline. This means that the rat, a big, white animal, was injected with some kind of anesthesia, and we watched it run around a plastic tub until it became loopy and clumsy and finally lay still. We then placed it on a board and drove pins through its paws, crucifixion-style. We looped a string over his front teeth to hold his head back. We took shiny thin scissors and cut into the animal's skin and right through his ribcage. Inside the ribcage was the dark-red, still-beating heart.

Blood starts to clot in the brain as soon as an animal dies. To get clean slices of brain, we had to push the blood out while the animal was still alive.

The heart is, of course, connected to all the blood in the body. When the left ventricle contracts, blood is pushed into the aorta; it goes from the aorta into smaller arteries and arterioles; from there, it goes into the tiny thin capillaries and donates oxygen to tissue; and then it goes back, from all the rest of the body, into the veins and from there into the right atrium of the heart.

To perfuse an animal with saline, you insert a needle into the left ventricle of the still-beating heart, and you cut the right atrium of the heart with scissors. Then you push your solution through. As you push, saline travels the same route as the blood, and blood followed by saline exits through the right atrium of the heart. Quickly, the liver blanches and the paws, nose and tail become pale. The animal is entirely bloodless. The brain will be free of contaminating blood.

I understand that people become used to anything, eventually, no matter how horrifying. I’ve seen how medical students enter the anatomy lab for the first time. Their cadaver’s hands and face are covered with black plastic and the lower body is draped; all they can see is a torso. Still, they are silent and serious, and their cheeks flush pink. Sometimes people faint or vomit.

But a week later you’ll see them chatting and laughing with their lab partners as they wiggle their fingers around the vessels of the heart. A few months later they’ll dissect the face without any hesitation. They’ll prop the head up on blocks for better access and get to work on the forehead and cheeks and neck, complaining about the number of tiny structures they have to memorize, talking about how much they love to use the bone saw. They act like completely different people than the ones who entered the lab only months before.

Strangely, I’ve had the opposite reaction to animal work. In the beginning the difficulty of the procedures absorbed my thoughts, so it didn’t occur to me to react to what I was doing. Now, the tasks seem simple, so I have plenty of time to observe the crucifixion of a mouse, the insertion of a needle into a heart the size of a jellybean, the blood spreading out beneath the small body like dark angel wings.

Now it seems to me no coincidence that the most famous martyr of all time was not hanged or burned at the stake, but crucified.

From three years of graduate school I have learned to handle mice like a musician handles an instrument. I can reach into a cage without flinching, grab a tail, take the animal in a firm grip, inject something into the peritoneum or force-feed the mouse with a tube down the throat, and drop it back into the cage. The mice barely react. Once an animal is dead I can remove anything: spleen, liver, brain, spinal cord, bone marrow, cardiac blood – even the tiny pale lymph nodes buried under its little arms.

I don’t even notice how easily I handle mice until I see a new student reach tentatively into the cage and pull her hand back quickly, as if the mouse were extremely hot.

Sometimes I imagine there is a circle of hell for people like me. There I will gasp in chambers full of ether or carbon dioxide; my neck will be snapped, repeatedly, and my lymph nodes removed; or I will be forced to watch as humans are cut open and perfused, their heads flopping on their bloodless bodies, before I am lifted by a gigantic hand and pinned to a board to share their fate.

Of course, if I have to pay for each mouse I killed, then I should also pay for every chicken that has died for my dinner. At least laboratories have ethics boards to ensure that we cause the animals as little discomfort as possible. The meat-producing industries have no such boards, and minimal distress gives way to quick and easy every time. They can dock tails without anesthesia, keep animals packed in together, feed them unnatural foods: any number of things that I am forbidden to do to my mice.

When the mouse went skittering across our kitchen floor, my husband thought I should be the one to take care of it. "Isn't this what you do all day?" he asked.

The mouse looked different from the mice I work with: scrawnier, dirtier. There is a world of difference between a mouse in the confines of a cage, a mouse who has lived all his life in a clean laboratory setting, and a scrawny wild mouse who is running behind your stove. I pulled up my feet and shrieked like a girl.

He went and bought traps.

I could never use traps on my laboratory-bred mice, whether mechanical or glue. There is too much potential for discomfort. We anesthetize with carbon dioxide, then snap their necks. And yet I can use any method I want to dispose of a mouse in my home.

The ethics boards have determined even the language scientists use. At home I kill mice; in the lab I 'sacrifice' them. In everyday conversation this is shortened to sac’ing: as in, did you sac those heterozygotes today?

But if you ask my husband what I do all day, he says "She kills mice." Sometimes he says, "She gives mice MS."

In the lab we call the multiple sclerosis-like mouse model I study experimental autoimmune encephalomyelitis, or EAE. Although this model resembles MS in some ways, it is not MS. My work is in basic immunology, studying cellular interactions in this mouse model of autoimmunity. The work I’m doing isn’t really pursuing a cure, although it is possible that my work could someday lead to some other research that would lead to a study that would lead to a treatment.

Is it wrong that I sacrifice hundreds of mice without seeking to cure a disease?

Most cosmetic companies stopped using animals for testing back in the 1980s. Their customers were upset that cute bunnies and gerbils suffered for a better shampoo, and besides, we already knew what sodium lauryl sulfate did to the eye.

I thought my rodent work was different than that. The animals I used in research went for a better purpose than a non-carcinogenic lipstick: they were sacrificed to save human lives. Now I know how many animals die in experiments that don’t work or that are poorly designed. Now I know how many animals are bred accidentally along the way and have to be sac’d just for existing. And even when experiments are well-planned and successful, can we justify the death of a mouse for basic science? How many mice can we justify for experiments that may, someday, lead to a better life for someone? Ten thousand mice per person saved? One million?

The third time I worked with rodents I studied circadian rhythms in mice. Circadian rhythms can be important to people who work night shifts, and people with jet lag.

For centuries, the frontier of medical science was anatomy, and anatomy meant stealing bodies to cut open and tease apart. Now the knowledge gathered by generations of anatomists seems obvious, basic, almost trivial. They didn’t cure many diseases by quibbling about nerves and bones and the ventricles of the brain.

But if no one had mapped the arteries and veins, William Harvey wouldn’t have realized that the heart pumped blood through the body. Without knowing the path of each tiny nerve, William Bayliss and Ernest Starling couldn’t have determined the existence of hormones, and Otto Loewi couldn’t have discovered neurotransmitters. Without the basic understanding of how organs connected, it would have been impossible to figure out the elaborate systems of physiology – and to figure out how to fix the things we can.

Maybe I am poking around in mice like the anatomists did in corpses, performing the most basic experiments so one day someone can make a great leap. Just as Galen and Vesalius could never have predicted endocrinology, neuropharmacology or DNA, how can I predict now where the pieces I uncover will lead? We have no choice but to describe what we see in front of us until we develop a bigger picture.

The mouse in front of me, unconscious, little arms pinned straight out to the side, doesn’t know this reasoning, and she probably wouldn’t consent if she did. She would probably tell me I am justifying my actions, and that even if everyone does this kind of research it doesn’t mean it’s the best way to move science forward. I snip through her skin, I cut through her ribcage, I insert a needle into her tiny, still-beating heart. I hope that the demons in my circle of hell will try to be gentle too.