An historical question

Does anybody know who first defined the general notion of representable functors? Here is what I have: Mac Lane in his book says that the notion appeared in topology under the name "universal exa mples" and refers to a paper by Serre published in 53. In their book on homological algebra, Cartan and Eilenberg talk about "a representation of A" for sums and products only, and although no functor is mentioned. Grothendieck does essentially the same in his Tohoku paper. I do not have access to Yoneda's 1954 paper where it might appear explicitly. So, what it the story? Thanks, Jean-Pierre Marquis 21-Aug-2002 10:42:03 -0300,1171;000000000001-00000000