… we may, I think, without much rashness, assume that there is some substance or substances in the nerve endings or gland cells with which atropin and pilocarpin are capable of forming compounds. On this assumption then the atropin or pilocarpin compounds are formed according to some law of which their relative mass and chemical affinity for the substances are factors. In the analogous case with inorganic substances, other things being equal, these are the sole factors. To take the simplest case, if a and b are both able to form, with y, the compounds ay, by, then ay and by are both formed, quantity of ay and by depending on the relative masses of a and b present and their relative chemical affinity to y[14].