"[The basic stumbling block] did not lie in the mechanical or optical part of the apparatus, but on the electrical side of the problem, and essentially in the light sensitive cell. I made many attempts to improve this, including the construction of a cell made from the visual purple* out of a human eye. There was considerable difficulty in obtaining the eye, but at length I was fortunate in finding a surgeon with a keen scientific interest who supplied a fresh human optic. This cell when first constructed gave a quite appreciable reaction to light."Television. A Paper by Mr J L Baird', Experimental wireless and the Wireless Engineer, December 1926, pp.736 Quoted in: KAMM A, BAIRD M(2002) John Logie Baird; A Life. Edinburgh. National Museums of Scotland Publishing. pp.64
* Not a mistake... Scots for pupil I should imagine.