Homeopaths make their medicines by taking the ingredients, adding water, and shaking the mixture. They then take a drop of the mixture, throw out the rest, and add more water. They do this usually 30 times but sometimes up to 200 times. They call it potentisation. Hahnemann said this would bring out the "spirit-like medicinal powers held within a drug". Science can show how many atoms or molecules—tiny things that cannot be divided up any more—of the original substance are left in the homeopathic drug. In most homeopathic drugs, there is not a molecule left of the substance they started out with. Homeopaths believe that the solution carries a "memory" of the original substance. Science says that goes against the laws of physics and chemistry.