In the early days of microbiology experiments, when researchers needed test subjects they frequently went to those closest nearby which included their family or themselves.
Now, we have animals to use for experimentation or humans, if the right permission is granted and protocols obtained.
That said, some modern biohackers, or people who take a do it yourself (DIY) mentality to science experiments, are going old school and using their own bodies as the first test subject. Recently, Aaron Traywick, CEO of Ascendance Biomedical, did just that. He injected himself on stage at the conference BodyHacking Con with a homemade herpes treatment.