There was a theory in the 80s that gastric ulcers were a psychosomatic problem caused by stress. Patients were given anti-depressants, antacids or psychotherapy. Doctor Marshall treated patients with antibiotics, and his results were the answer to the real problem. Marshall constructed the theory that the spiral-shaped Helicobacter bacterium was the culprit to gastritis. He used his body to experiment. His critical thinking led to combating Helicobacter.