The Red Thread of a CaseDespite their differences, Kent, Vithoulkas and Sankaran all attempted, in ascending degrees, to find the tonic side of disease by means of the genius of the case, the "red thread" that runs through the case history. This red thread was first mentioned by Boenninghausen in connection with the creation of general modalities out of particular modalities, an example of the application of thought to the pathic data in order to discern what is characteristic.
All of these indications are so trustworthy, and have been verified by such manifold experiences, that hardly any others can equal them in rank — to say nothing of surpassing them. But the most valuable fact respecting them is this: That this characteristic is not confined to one or another symptom, but like a red thread it runs through all the morbid symptoms of a given remedy, which are associated with any kind of pain whatever... (quoted in Close, The Genius of Homeopathy, Chapter XVI, p. 263; original italics)This term, the red thread, can also be found in Reich’s work on character analysis. The idea of the essence or of the spirit of a disease/remedy are just variations of the Hahnemannian idea of the characteristic aspect of a disease.