106     At first, about forty years ago, I was the only person who made the provings of the pure powders of medicines the most important of his occupations. Since then I have been assisted in this by some young men, who instituted experiments on themselves, and whose observations I have critically revised. Following these some genuine work of this kind was done by a few others. But what shall we not be able to effect in the way of curing in the whole extent of the infinitely large domain of disease, when numbers of accurate and trustworthy observers shall have rendered their services in enriching this, the only true materia medica, by careful experiments on themselves! The healing art will then come near the mathematical sciences in certainty.