This is one approach you could take on your historical paper on autism.

Begin your research with some background reading the topic of autism. I suggest an ebook found in our online catalog, Autism: mind and brain edited by Uta Frith and Elisabeth L. Hill. Early in the book (p. 21-23) a history is given with all of the major contributors to the understanding of autism. You could start with Hans Asperger's original account of "austistic psychopathy" in 1940 and leading up to the development of the criteria used in the DSM-IV today to diagnose autism.

Another book to look at is A history of autism: conversations with the pioneers by Adam Feinstein.

Once you find out who the major contributors are to the knowledge of autism you will want to search the databases Sage and ProQuest Social Science Collection to see what their contributions have been and how the understanding of autism has changed since 1940.