Here's a short story:

Unlike chemists and physicists, who usually do their experiments using machines, biologists and medical researchers have to use living things like rats. But there are three Nobel prize-winning scientists who actually chose to experiment on themselves - all in the name of science, reported The Telegraph. 1. Werner Forssmann (Nobel prize winner in 1956) Forssmann was a German scientist. He studied how to put a pipe inside the heart to measure the pressure inside and decide whether a patient needs surgery. Experiments had been done on horses before, so he wanted to try with human patients. But it was not permitted because the experiment was considered too dangerous. Not giving up, Forssmann decided to experiment on himself. He anaesthetized his own arm and made a cut, putting the pipe 30 centimeters into his vein. He then climbed two floors to the X-ray room before pushing the pipe all the way into his heart. 2. Barry Marshall (Nobel prize winner in 2005) Most doctors in the mid-20th century believed that _ was down to stress, spicy food or an unusually large amount of stomach acid. But in 1979 an Australian scientist named Robin Warren found that the disease might be related to a bacteria called Helicobacter pylori. So he teamed up with his colleague, Barry Marshall, to continue the study. When their request to experiment on patients was denied, Marshall bravely drank some of the bacteria. Five days later, he lost his appetite and soon was vomiting each morning - he indeed had gastritis. 3. Ralph Steinman (Nobel prize winner in 2011) This Canadian scientist discovered a new type of immune system cell called the dendritic cell. He believed that it had the ability to fight against cancer. Steinman knew he couldn't yet use his method to treat patients. So in 2007, when doctors told him that he had cancer and that it was unlikely for him to live longer than a year, he saw an opportunity. With the help of his colleagues, he gave himself three different vaccines based on his research and a total of eight experimental therapies. Even though Steinman eventually died from his cancer, he lived four and a half years, much longer than doctors had said he would. (End of story)

Provide your best guess for the following question. Give ONLY the guess, no other words or explanation.

For example:

Guess: <most likely guess, as short as possible; not a complete sentence, just the guess!>

Here are a few examples of questions and answers:

Question: Do chemists usually use rats for their testing?
Guess: yes

Question: Who uses rats?
Guess: biologists and medical researchers

Question: Who was Werner Forssmann?
Guess: German scientist

Question: when did he when the Nobel prize?
Guess: 1956

Question: what did he study?
Guess: He studied how to put a pipe inside the heart to measure the pressure inside and decide whether a patient needs surgery.

Question: Which human did he want to perform an experiment on?
Guess: himself

Question: was he supposed to?
Guess: No

Question: did he do it anyway?
Guess: Yes

Question: what did he do to his arm?
Guess: made a cut, putting the pipe 30 centimeters into his vein

Question: then where did he go?
Guess: X-ray room

Question: to do what?
Guess: pushing the pipe all the way into his heart

Question: Who was Ralph Steinman?
Guess: Canadian scientist

Question: did he discover something?
Guess: a new type of immune system cell

Now answer the following question in the same format.

Question: what was it?

the dendritic cell