Possible Clues:

• Radiation, e.g.
• It changes genes
• Briefly unable to talk to spy not finished producing arsenic, for one
• Blokes accepting university name for chemical substance?
• Bodily substance that could give men a gut
• Agent for change to get a stomach churning over — dope?
• Changing agent, as Greek character changing agent
• Turn magnet around, it causes change
• Agent that can induce genetic mutation
• Biochemical substance that could make me gaunt