No doubt the reason is that the joint can rest. The merciful influence
of pain in the part affected insures repose for each affected joint.
Suppose it were otherwise. Imagine pain absent and conceive for a moment
that we could flex and extend an acutely rheumatic knee or elbow sixty
or eighty times per minute continuously, what would be the fate of the
joint? Is there any probability that restoration to the normal condition
would follow? Few of us, I think, would expect it, for it is a
physiological law that repair in a diseased organ cannot coincide with
full functional activity. When the endocardium and valve cusps are
inflamed pain does not give the signal for rest, for, indeed, pain or no
pain, the toiling heart cannot intermit its labours.