Is when old symptoms are observed to reappear. In proportion as old symptoms that have long been away return just in that proportion the disease is curable.
They have only disappeared because newer ones have come up. It is quite a common thing for old symptoms to appear after the aggravation has come, and hence we see the symptoms disappearing in the reverse order of their coming.
Those symptoms that are present subside, and old symptoms keep coming up. The physician must know himself that the patient is on the road to recovery, and it is well to say to the patient that this is encouraging; that diseases get well from above downwards, etc.
Old symptoms often come back and go off without any change of medicine. It indicates that the medicine must be let alone. If the old symptoms come back to stay then a repetition of the dose is often necessary.