From a Google search tha sent to somewhere in Wikipedia:

Medical experiments

Draftees in Civilian Public Service became medical and scientific research test subjects in human medical experiments under the direction of the Office of Scientific Research and Development and the Surgeon General at medical institutions such as Harvard Medical School, Yale and Stanford Universities, and Massachusetts General Hospital. These experiments involved a range of research topics, sometimes endangering the health of the COs.[38][39]
Conscientious objector Harry Lantz distributes rat poison for typhus control in Gulfport, Mississippi.

Hepatitis: During the 1940s the cause, method of communication and treatment of infectious hepatitis was not well understood. Experimentation began with COs working at psychiatric hospitals and was expanded to a major research project with 30 to 60 test subjects at the University of Pennsylvania and Yale University. The men were inoculated with infected blood plasma, swallowed nose and throat washings and the human body wastes of infected patients, and drank contaminated water.[40]

As a young surgeon, C. Everett Koop was part of the research team at the University of Pennsylvania School of Medicine. He relates his experience with CPS test subjects:
"         And the first time I was introduced to this whole program when I as a young surgeon, was asked to do serial biopsies on their livers to see what the effect of the virus was in the production of the changes in the liver. And in that way, I got to know that a lot of these young men had no idea that the risk they were taking also included death. And some of those youngsters did die and it was a very difficult thing for me to be part of, because you know, you're powerless, when you're part of the big team.

It couldn't happen today. Internal Review Boards would not permit the use of a live virus in human subjects unless they really understood what was going to happen to them. And I doubt that even if they knew what the risk was, that an Internal Review Board in any academic institution would consent to that kind of experimental work.
        "

—C. Everett Koop[41]

The hepatitis research was instrumental in determining a virus is responsible for the disease and that it is transmitted through human filth, serum and drinking water.[40]