In cases of yellow fever or cholera, assuming the rest of the pathogenesis is similar, the black vomit is the most important symptom initiating the choice of Cadmium sulphuratum. The forceful and persistent vomiting that tends to be black is the main guiding symptom for this remedy. It is often accompanied by burning and cutting pain in the stomach, excessive salivation, and intense nausea accompanied by violent retching and gagging. Once the extreme prostration, the desire to lie down quietly and undisturbed, is added, the picture of yellow fever or cholera becomes complete. Indeed, Hering relates the successful use of Cadmium sulphuratum in a murderous epidemic of yellow fever. An additional striking symptom that usually occurs in Cadmium sulphuratum cases is general chill, which is so deep that it cannot be ameliorated even if the patient stands near a heater.
Frequently the practitioner gets the idea of the indicated remedy simply by looking into the overall pathological history of the case.
There are numerous examples where one problem disappears only to be replaced by another and the specific pattern indicates the appropriate remedy. For example, if you see a case with a persistent skin eruption where eventually the eruption is ‘cured’, but then a duodenal ulcer sets in, think of Graphites. If a skin eruption disappears and epileptic convulsions set in, then the first remedies to think of are Zincum and Causticum. If skin eruptions disappear and then a chorea manifests, think of Staphysagria or Agaricus. If injuries are followed by an epileptic attack, think of Arnica. If mental problems, especially depression, follow injuries to the head, think of Natrum sulphuricum.
Every remedy has its own preferred steps for the development of its pathology. The differences may be subtle, but this subtle differentiation can be learned through the study of the materia medica. What is important to understand is that each organism has specific sensitivities in its different layers and what we are trying to do is to match these sensitivities with the pathogenesis of the remedy as a whole.