Speculations and experiments with regard to the elixir of life, the philosopher's stone, and the transmutation of metals, are presumed to have filled up all the serious interests of the alchemists, supposed to be almost the only scientists of those days. As a matter of fact, however, men were making original observations of profound significance, and these were considered so valuable by their contemporaries that, though printing had not yet been invented, even the immense labor involved in the manifold copying of large folio volumes by the slow hand process did not suffice to deter them from multiplying the writings of these men so numerously that they were preserved in many copies for future generations, until the printing press came to perpetuate them. Of this there is abundant evidence in the preceding pages as regards medicine, and, above all, surgery, while a summary of accomplishments of workers in other departments will be found in Appendix II, "Science at the Medieval Universities." At the beginning of the twentieth century, with some of the supposed foundations of modern chemistry crumbling to pieces under the influence of the peculiarly active light thrown upon our nineteenth century chemical theories by the discovery of radium, and our observations on radio-active elements generally, there is a reawakening of interest in some of the old-time chemical observers, whose work used to be laughed at as so unscientific, or, at most, but a caricature of real science, and whose theory of the transmutation of elements into one another was considered so absurd. It is interesting in the light of this to recall that the idea that the elementary substances were essentially distinct from each other, and that it would be impossible under any circumstances to convert one element into another, belongs entirely to the nineteenth century. Even so deeply scientific a mind as that of Newton, in the preceding century, could not bring itself to acknowledge the tradition, that came to be accepted subsequent to his time, of the absurdity of metallic transformation. On the contrary, he believed quite formally in transmutation as a basic chemical principle, and declared that it might be expected to occur at any time. He had seen specimens of gold ores in connection with metallic copper, and concluded that this was a manifestation of the natural transformation of one of these yellow metals into the other.