Introduction to the original article. Dr Pio del Rio-Hortega has been working 'temporarily' in a little laboratory in La Residencia for the past 15 years. With exemplary perseverance and goodwill, he has carried out, in this little corner, a labour that has been greatly appreciated by researchers throughout the world, but is perhaps not sufficiently recognized among ourselves. Through the use of original methods he has been able to make visible the most delicate details of the structure of cells. His research on the histology of the nervous system led him to discover a new species of cells, which the scientific world has baptized, in his honour, with the name of 'Hortega cells'. His uninterrupted line of investigation continues with research on tumours of the nervous system, on which he was confirmed as the leading authority at the last International Conference on Cancer. Dr Rio-Hortega is a devotee of the visual arts, and a fruit of the marriage between his enthusiasm for art and his scientific activities is the article that follows.