Warning This Section Does Contain Spoilers
The journal followed Sydney Cooper as he mapped a parcel of land in West Virginia for the Strahlenberg Mining Company between the dates of 1873 and 1906. After solving all of the cyphers in the journal, see how to do that here, I plugged all those solved sentences in where they belong in the journal to make the journal complete. He mentions the "glowing vein" and that he can hear it vibrating at night, even in his dreams. After finding this "glowing vein" Sydney Cooper goes into a manic type state with no sleeping or eating. As a reader we aren't sure if he has a legitimate psychiatric diagnosis or if the glowing vein is causing this. He is claiming that things are moving, glowing, his memory is not the same, aggression or irritability, loss of appetite, loss of time, paranoia, muscle tremors, and delusions. He was in a cave with bats and kept one as a pet and could have very easily gotten bitten by one and contracted rabies which would cause all of these symptoms. He goes to the camp doctor and the doctor inspects him for French Disease (see link below), which is another name for syphilis, but the doctor just gives him mercury pills that Sydney doesn't take. Instead he takes toxic mushrooms that cause hallucinations.