The majority of the test subjects, otherwise known as "logs " for the medical assistants to cope more easily, were Chinese. But overall the Japanese tested anyone they could get their hands on which also included Russian, Korean, Mongolian, Pacific Islander, Southeast Asian, and even a few American victims but of all the thousands of POW's taken to Unit 731, not a single prisoner survived (Keiichi). The causes of death for these prisoners was numerous, cruel, and never painless. They ranged from being cut open without anesthetics, to standing out in the cold waiting for their limbs to freeze, to being locked inside pressure chambers to test how much the body could take before their eyes popped out. Many experiments tested diseases. A man with a disease would be placed into a cell with a man without the disease, and the doctors would observe how long it would take for the disease to spread. After the disease had spread, they would take the man with the new disease and surgically look at what the disease had done to the man's inside to search for ways to cure it. During all surgeries, no anesthetics were used in fear of it altering the results. (Blumenthal) .
Not only were experiments done inside the surgical room but also outside of it. The bitter cold Manchurian winters were hard on Japanese troops; therefore, doctors wanted to find the best way to treat frostbite, and they did. The doctors proved that the best treatment for frostbite was to immerge the limb in water a bit warmer than 100 degrees, but never more than 122 degrees. (Stringer) The cost of this scientific breakthrough was paid by those used for medical experiments. They were taken outside and left with exposed arms, periodically drenched with water, until a guard decided that frostbite had set in. Testimony from a Japanese officer said this was determined after the "frozen arms, when struck with a short stick, emitted a sound resembling that which a board gives when it is struck.