Abelian Categories: an Introduction to the Theory of Functors by Peter Freyd
Publisher: Harper and Row 1964
Number of pages: 192
From the table of contents: Fundamentals (Contravariant functors and dual categories); Fundamentals of Abelian categories; Special functors and subcategories; Metatheorems; Functor categories; Injective envelopes; Embedding theorems.
Mathematics Category Theory