In 2013, a new hypothesis was proposed. Ronald Hamilton, a retired bookbinder at the Indiana University of Pennsylvania, suggested a link between the symptoms described by McCandless and the poisoning of Jewish prisoners in the Nazi concentration camp in Vapniarca. He put forward the proposal that McCandless starved to death because he was suffering from paralysis in his legs induced by lathyrism, which prevented him from gathering food or hiking. Lathyrism may be caused by ODAP poisoning from seeds of Hedysarum alpinum (commonly called wild potato). The ODAP, a toxic amino acid, had not been detected by the previous studies of the seeds because they had suspected and tested for a toxic alkaloid, rather than an amino acid, and nobody had previously suspected that Hedysarum alpinum seeds contained this toxin. The protein would be relatively harmless to someone who was well-fed and on a normal diet, but toxic to someone who was malnourished, physically stressed, and on an irregular and insufficient diet, as McCandless was. As Krakauer points out, McCandless' field guide did not warn of any dangers of eating the seeds, which were not yet known to be toxic. Krakauer suspects this is the meaning of McCandless' journal entry of July 30, which states, "EXTREMELY WEAK. FAULT OF POT[ATO] SEED. MUCH TROUBLE JUST TO STAND UP. STARVING. GREAT JEOPARDY."