The substance that causes Barbara to have gout is uric acid that builds up in her blood (plasma).
Gout disease is a type of arthritis that occurs when uric acid builds up in the blood (plasma) and causes inflammation in the joints.
In Barbara's case, this uric acid buildup is affecting her big toe joint, so she has more pain there.
Learn more about gout in: https://brainly.com/question/11520652
#SPJ12