Classical homeopathy is generally defined as a system of medical treatment based on the use of minute quantities of remedies that in larger doses produce effects similar to those of the disease being treated. It is believed that very small doses of a medication could have very powerful healing effects because their potency could be affected by vigorous and methodical shaking. This is referred to this alleged increase in potency by vigorous shaking as dynamization. It is also thought succussion could release immaterial and spiritual powers, thereby making substances more active. Tapping on a leather pad or the heel of the hand was alleged to double the dilution. Examples include: the use of an isopathic (disease associated) agent as a first prescription in a stuck case, when the beginning of disease coincides with a specific event such as vaccination; the use of a chemically related substance when a remedy fails yet seems well-indicated; and more recently, the use of substances based on their natural classification (the periodic table or biological taxonomy). This last approach is considered to be promising by some in the homeopathic community, because it allows for grouping remedies and classifying the ever-burgeoning Materia Medica, but is rejected by many purists because it involves speculation about remedy action without proper provings.