I have seen stools before (but not like this one) and they are actual known as a "gouty stool" which can change elevation. This one looks to be lightweight for travel for someone afflicted with it (and would make sense to have a bus tag on it.)
The ones I am more familiar with are solid or are the "scissor" mechanism ones.
Gout was very prevalent among the "well-to-do" and those with predominantly animal/meat/poultry diet, and most often in history for those that were over-weight (which isn't necessarily so these days but due to high acidity in the body and a predisposition to it). From history, Gout has been known as "The disease of Great Kings", "The disease of the Wealthy" and "The Rich Man's Disease" due to the fact they had more fat content due to their diets and lifestyles. Today it is referred to as a type of arthritis cause by high acidity levels in the body and can be controlled by diet and exercise! (Can you tell I have a family member that has experienced gout:!:!)
They not only made gouty stools of various forms they had "gouty chairs". As found in this mansion (A Harewood House Inventory, 1795) "Yet the Merlin’s Gouty Chair in the coffee room below may serve to remind us of how rich eighteenth-century diets played havoc with the body. "
